PART 1.. The Heart and Blood-Vessels.

THE HEART AND BLOOD-VESSELS.

I. THE HEART.

(The original arrangement of this section has been modified.)

The heart is situated in the middle line above the central portion of the shoulder-girdle and M. sternohyoideus, and below the oesophagus; the apex is directed backwards and lies between the lobes of the liver, the base is directed forwards and lies a short distance behind the larynx. The heart is surrounded by the pericardium.

A. The *Pericardium* [is a very thin membranous sac, which completely encloses the heart; it is attached, at some distance, to the large vessels passing to and from the heart, and has inserted into it some fibres of the M. obliquus abdominis internus (see page 70). A fold of the pericardium extends from the dorsal surface to the truncus arteriosus, and through it courses the vena cardiaca.

The heart and blood-vessels, seen from the ventral surface; after Howes.

AC. Left anterior caval vein. C′. Carotid arch. LA. Left auricle. P′. Right pulmo-cutaneous arch. RA. Right auricle. S′. Left systemic arch. TA. Truncus arteriosus. V. Ventricle. ]

The pericardium is a connective-tissue membrane, and is lined on either side with endothelium, which is in part ciliated (Leydig); the endothelium of the inner surface is continued on to the heart and so forms a closed lymph-sac. The pericardium is more or less pigmented, and contains both vessels and nerves; it may contain fat-cells].

B. The *Heart*.

The heart, seen from above, and dissected to show the opening from the Sinus venosus to the right auricle; after Howes.

C′. Right carotid arch. IC. Posterior caval vein. LA. Left auricle. P′. Right pulmo-cutaneous arch. PV. Pulmonary vein. RA. Right auricle. S′. Right systemic arch. SV. Sinus venosus. SV′. Opening of Sinus venosus into the right auricle. V. Right anterior caval vein. ]

*a.* The *Sinus venosus* (Sinus venarum cavarum), (Fig. 133 SV.) is a thin-walled sac lying on the dorsal surface of the heart, and very slightly to the right side (Hoffmann). It is somewhat triangular in form, receiving an anterior caval vein at each anterior angle (V.), and the posterior caval vein (IC.) at the posterior angle. The ventral wall has a transverse opening (SV′.), by which it communicates with the right auricle; the opening possesses two valves, an anterior and a posterior, and is placed close to the auricular septum.

*b.* The *auricles* [are not always separated, as the septum which usually brings about the separation is in some cases incomplete, and in rare instances appears to be absent (Hoffmann)]; according to Ecker, the auricular septum is sometimes placed so far to the left side that it appears to be absent (Fig. 135). The septum is attached to the walls of the auricles so as to form two distinct cavities, which communicate at the auriculo-ventricular opening, where the septum has a free concave border (Fig. 134). The right auricle is much larger than the left, and receives the systemic venous blood from the sinus venosus by the opening (Figs. 133 and 134 SV.) already described. The left auricle receives the blood from the lungs by the pulmonary vein (Fig. 133 PV.), which opens into the auricle near the septum (Fig. 134 PV.): [the openings from the sinus venosus and from the pulmonary vein may be so closely approximated as to be separated by the septum only. The septum is much thinner than the auricular walls]. Both auricles open into the ventricle by the auriculo-ventricular opening (Fig. 134).

The frog’s heart seen from the ventral surface, and dissected so as to show its structure. The ventral walls of the truncus arteriosus and of the auricles and ventricle have been removed. From a drawing by Mr. Hurst.

A. Auriculo-ventricular aperture and valve. B. Aperture leading from ventricle to truncus arteriosus. C. Left carotid arch. LA. Left auricle. P. Left pulmo-cutaneous arch. P′. Style passed down right pulmo-cutaneous arch into the truncus arteriosus, T. PV. Opening of pulmonary vein. RA. Right auricle. S. Left systemic arch. SA. Septum atriorum. SV. Opening of Sinus venosus into right auricle. V. Ventricle. ]

*c.* The *ventricle* (Figs. 132, 134, and 136 V.), examined while still living, is seen to be bluntly conical in shape and darker on the left side than on the right; this is due to the ventricular wall of the right side, near the truncus arteriosus, being somewhat thinner. The inner wall is not smooth but possesses muscular ridges (Trabeculae). At its base the ventricle communicates with the auricles by the auriculo-ventricular opening (Figs. 134 and 136), and with the truncus arteriosus by a separate opening (Fig. 134 A.). The ventricle is lined by a layer of endocardial endothelium.

Dissection of a case in which the auricular septum is placed more to the left than is normal.

S Septum. SS Left auricle. V Opening into the Sinus venosus. ]

Dissection of the heart from the left side; after Howes.

A. Auriculo-ventricular opening. AC. Anterior caval veins. IC. Posterior caval vein. LA. Left auricle. PV. Pulmonary vein. RA. Right auricle. SV. Sinus venosus. TA. Truncus arteriosus. V. Ventricle. ]

The *auriculo-ventricular opening* (Fig. 134 A.) is a large aperture guarded by two valves, a dorsal and a ventral: each valve is formed by a reduplication of the endothelium, and contains a small amount of connective-tissue; its free margin is bound down by a number (about twelve) of fibrous cords, the chordae tendineae, which are attached by their posterior extremities to the trabeculae.

*d.* The *truncus arteriosus* (Figs. 132 TA., 134 A.) arises at the base of the ventricle, on the right side of its ventral surface, then passes forwards and to the left, across the auricles, to reach their anterior border near the median line, where it divides to form two vessels.

Internally it is incompletely divided into two compartments by a spiral valve (Fig. 134); the valve is attached to the dorsal surface and is free ventrally: when the vessel is fully dilated (artificially), the valve extends two-thirds of its diameter. The opening of the vessel into the ventricle is guarded by two semilunar valves (Fig. 134 A.), the free margins of which are bound to the inner surface of the tube by chordae tendineae. The distal extremity has a semi-lunar valve in the left compartment (Fig. 134), which is attached by a delicate band to the spiral valve (Ecker).

C. *The minute structure of the Heart.*

*a.* The *muscular structure* of the heart.

(1) The *arrangement* of the *muscle-fibres* varies in the different portions of the heart. That of the ventricle will be easily understood by reference to Fig. 137. A layer of circular fibres (CM) extends round the whole ventricle, and from it more or less radial or transverse bands (TM, also Fig. 138 TM) pass inwards; these, in the apical portion of the ventricle, seem to extend almost transversely across; towards the base they are directed onwards and forwards towards the auricles. Of these bands some, near the apex, can be traced directly to the opposite side, others join the wall more anteriorly, and still others join bands of muscular fibres (LM), which may be described as longitudinal, and form the Musculi papillares. In the anterior portion of the ventricle the same arrangement holds good, but is modified to form a central cavity; still more anteriorly, at the junction of auricles and ventricle, the trabecular structure is much less apparent, the fibres being closer and mainly circular.

I. Transverse section through the junction of the hinder and middle thirds of the ventricle of R. temporaria. II. Transverse section through junction of middle and anterior thirds of the same heart. Occ. I, Syst. 1, Leitz. The heart was freely distended with dilute spirit, and so hardened.--G. H.

CC Central cavity. CM Circular muscle. LM Longitudinal muscle. TM Transverse muscle. ]

In the auricles the muscular fibres are chiefly arranged in circular rings which cross one another; on the inner surface, however, traces of an arrangement similar to that in the ventricle may be made out. In the heart, from which the sections in Fig. 137 were drawn, transverse bands (cut longitudinally), 0.33 mm. in length, were numerous; their central ends terminated in bands, the fibres of which were cut transversely. The auricular septum (Fig. 141 a M) also possesses muscular fibres which cross one another in its substance.

The fibres of the truncus arteriosus resemble those of an ordinary artery; those of the sinus venosus are arranged in rings, mostly transverse, but others oblique, and a few longitudinal.]

(2) The *structure* of the *cardiac muscle-fibres* (Figs. 138 and 141 a).

Portion of a transverse section through the middle of the ventricle of R. temporaria. From same heart as the sections in Fig. 136. Oc. I. Syst. 7, Leitz.--G. H.

A Rod-shaped nuclei of muscle fibre. B Oval nuclei of muscle fibre. CM Circular layer of muscle. CT Connective-tissue. E Endothelium of the epicardium. TM Transverse bands of muscle. ]

α. Cells with a broad nucleus (Fig. 138 B): the nucleus is lenticular or egg-shaped, 4 to 7 µ broad, 8 to 14 or 18 µ long; the ratio of length to breadth being 1 : 2.

β. Cells with a narrow nucleus (Fig. 138 A): the nucleus is rod-shaped, 2·5 to 3·5 µ broad and 25 to 43 µ in length. The ratio of length to breadth varying from 1 : 8 to 1 : 16. These cells are more frequent in the right half of the base of the ventricle than the former variety. In the trabeculae the second variety is more numerous (Pohl-Pincus).

The muscle-fibre may be simple (Fig. 141 a M) or possess branches (Fig. 138); the fibres are all more or less spindle-shaped, and striated transversely and longitudinally, but possess no sarcolemma. The protoplasmic contents of the cell are finely granular; the nucleus much more coarsely granular and possessing one or more distinctly marked nucleoli. The striations are due to the presence of a network, which has been carefully described by Messrs. B. Melland and C. F. Marshall, and is similar to that of ordinary voluntary muscle (see histology of muscle).]

*b.* The *nerves* of the *heart*.

The nervous supply of the heart is derived from the sympathetic system and from the cardiac branches of the pneumogastric nerve; the course of which has already been traced (page 175) to the roots of the anterior caval veins, where they form a simple plexus by means of a connecting link (Fig. 139). The plexus possesses nerve-cells and sends off two nerves into the auricular septum; the one (d) lies dorsally and is shorter and thicker than the other (v), which lies ventrally in the septum. They course backwards to the posterior border of the septum, and there distribute fine branches to the base of the ventricle and surrounding parts.

Course of the cardiac nerves in the auricular septum.

d Dorsal nerve. v Ventral nerve. ]

The nerve-fibres are both medullated and non-medullated. The nerve-cells (Figs. 139, 140, 141) are usually oval, and are unipolar or rarely bipolar; sometimes two cells exist in the same envelope, forming the ‘twin-cells’ of Dogiel (Fig. 141 b II). According to the recent observations of Lavdowsky and Dogiel each cell receives one medullated fibre and gives off a fine non-medullated fibre; the two run together for a short distance, after which the non-medullated fibre separates to supply muscle-fibres.

Group of nerve-cells on the cardiac nerve, from the auricular septum. Stained with picrocarmine. Occ. III, Syst. 3, Hartnack; after Dogiel.

F Fibres of the cardiac nerve. G Nerve-cells. ]

Two large clusters of nerve-cells have received special names.

*Remak’s ganglion* is a large group of nerve-cells in the wall of the sinus venosus.

*Bidder’s ganglion* is formed, collectively, by groups of cells in the auriculo-ventricular groove, the chief groups being attached to the two cardiac nerves.

No nerve-cells have been discovered behind that portion of the ventricle near the auriculo-ventricular groove, nor has a direct connection between the cells or their processes with the fibres of the pneumogastric nerve been made out.

Nerve-fibres have been described as existing in all parts of the ventricle and being connected with the muscle-fibres (Openchowsky and others); this cannot, as yet, be accepted as proved.

The truncus arteriosus also possesses nerve-fibres and nerve-cells (Pagliani, Löwit, and others), but their arrangement seems to be very irregular. Löwit did not succeed in finding the nerve-cells in all cases examined; and Engelmann denies their occurrence.]

*c* and *d*. [The *endothelium* and *connective-tissue* of the heart.

The connective-tissue of the heart exists only in very small quantity. A fine layer on the outer surface of the ventricle, especially towards the auriculo-ventricular groove, can easily be seen (Fig. 138 CT); the various valves, the auricular septum, and more particularly the truncus arteriosus, all contain connective-tissue. In the latter part the spiral valve is wholly formed of this tissue.

Small group of nerve-cells from the auricular septum. Stained with picrocarmine and silver nitrate, after Dogiel.

E Endothelium (endocardium). G Nerve-cells. M Muscle-fibres. N Nucleus. N′ Nucleolus. ]

Isolated nerve-cells from frog’s heart. I. Usual form of nerve-cell. II. ‘Twin-cell.’

C Capsule. N Nucleus. N′ Nucleolus. P Process. ]

The whole of the inner surface is lined with endothelium (endocardium), which covers the various trabeculae; the external surface of the heart is likewise covered with an epicardial layer of endothelium (Fig. 138 E).]

Arteries and veins of the Truncus arteriosus of Bufo vulgaris, after Hyrtl.

a Arteria bulbi. b Truncus arteriosus. h, i Hepatic portal veins. t Right and left synangium. v Vena bulbi anterior. vi Left innominate vein. vc Vena bulbi posterior (V. cardiaca). A Right auricle. A′ Left auricle. V Ventricle. ]

*e.* The blood-supply to the heart.

With the exception of the truncus arteriosus, no part of the heart possesses blood-vessels (Hyrtl). [The truncus arteriosus (Fig. 142 b) has a rich anastomosis, which receives its blood by the arteria bulbi (a), a branch of the carotid arch. Two veins connect this anastomosis with the systemic veins, and with the hepatic portal veins: the former, vena bulbi anterior (v), passes over the auricles to open into the left innominate vein (vi); the latter, the vena bulbi posterior (vc) or vena cardiaca, as it is more usually named, passes from the truncus arteriosus in a fold of pericardium, and then courses backwards to open into the anterior-abdominal vein.]

II. THE ARTERIES.

(The original arrangement of this section has been modified.)

The Truncus arteriosus divides to form two vessels (Figs. 132, 134); each of these is divided by two partitions into three compartments, which after a short course together separate to form three distinct vessels, the carotid, systemic, and pulmo-cutaneous arches.

*1.* The *carotid arch* (Canalis carotico-lingualis, Brücke; Ductus caroticus), (Fig. 143 I) is the most anterior of the three arches: it winds round the side of the oesophagus as far as the carotid gland, where it divides to form two branches; the right carotid arch gives off a small branch to the Truncus arteriosus, the Arteria bulbi (see above).

Schema of the arterial system of Rana esculenta.

A Dorsal aorta. c Cutaneous artery. ca Carotid artery. d Carotid gland. ic Iliac arteries. ie External iliac artery. ii Internal iliac artery. J Mesenteric artery. l Lingual artery. o Occipital artery. ov Occipito-vertebral artery. P Pulmonary artery. s Subclavian artery. T Truncus arteriosus. ug Urinogenital arteries. v Vertebral artery. I Carotid arch. II Systemic arch. III Pulmo-cutaneus arch. ]

The *carotid gland* (Fig. 144 c′) is a dilated portion of the vessel. The interior contains bands or trabeculae of muscle, which give its walls a more or less spongy structure; the muscle-fibres are not transversely striated (Hoffmann).

*a.* The *lingual artery* (Arteria lingualis, Arteria hyoidea-lingualis, Arteria hyoidea), (Figs. 143 l, 144 L) arises by two roots from the inner surface of the carotid gland, and courses forwards and inwards, supplying branches to the thyroid gland and the Musculi geniohyoidei, to the ventral surface of the hyoid; another continues forwards on the outer border of the M. hyoglossus to supply branches to the hyoid and tongue.

*b.* The *carotid artery* (Arteria carotis communis), (Figs. 143 ca, 144 c″) arises by several roots from the outer wall of the carotid gland; and passes over the Musculus petrohyoideus I to the anterior end of the oesophagus, round which it courses towards the vertebral column, and then runs forwards to the base of the skull. The artery then courses forwards, lying immediately above the mucous membrane and underneath the transverse arm of the parasphenoid, which it crosses about midway between its back and external end; [at this point the artery gives off two palatine arteries, then ascends in the orbit to the origin of the M. pterygoideus, and divides into two branches, the internal carotid artery and the ophthalmic artery]. The branches are:--

(1) The pharyngeal artery (Arteria pharyngea ascendens), (Fig. 145 p) which runs towards the opening of the Eustachian tube, distributes branches to the pharynx, and anastomoses with the Arteria pharyngeo-maxillaris of the cutaneous artery, and with the Ramus inframaxillaris of the occipital artery.

Right carotid gland.

c Carotid arch. c′ Carotid gland. c″ Carotid artery. L Lingual artery. ]

(2) [The posterior palatine artery (Arteria palatina posterior, Virchow) immediately divides into a number of small twigs to supply the mucous membrane of the hinder and outer parts of the gums.]

(3) The anterior palatine artery (Arteria palatina anterior, Virchow; Arteria palatina, Ecker), (Fig. 145 p′) runs forwards, between the Musc. levator bulbi and the mucous membrane, with the Ramus palatinus of the trigeminal nerve. [On reaching the palatine bone, it curves outwards to the outer anterior angle of the orbit, where it gives off a branch backwards along the upper jaw to the hinder portion of the orbit.] In its course it supplies twigs to the surrounding tissues, but chiefly to the mucous membrane and Harder’s gland.

Arterial system of Rana esculenta.

A Dorsal aorta. Ad Right systemic arch. As Left systemic arch. c (opposite fore-limb) Carotid artery. c (in abdomen) Coeliac artery. cm Cutaneous artery. e Lingual artery. H Heart. H′ Harderian gland. L Liver. Lu Lung. m Mesenteric artery. M Stomach. M′ Spleen. o Ophthalmic artery. p Pharyngeal artery. p′ Anterior palatine artery. S Subclavian artery. I Carotid arch. II Systemic arch. III Pulmo-cutaneous arch. ]

(4) The internal carotid artery (Art. cerebralis, Virchow); see Arteries of Brain, p. 162.

(5) The ophthalmic artery (Art. ophthalmica), (Fig. 145 o) [is larger than the internal carotid artery at this point; it crosses the origins of the M. rectus externus and of the M. retrahens bulbi and reaches the optic nerve; the artery then runs forwards along the under surface of this nerve and of the eyeball, lying close to the sclerotic coat as far as a little beyond the equator, where it pierces the sclerotic coat so obliquely that the choroid coat is only reached at the ciliary processes. In its course the artery supplies:--

α. Muscular branches, given off at the point where the artery reaches the eyeball.

β. Two arteries (AA. ciliares) to the choroid, given off at the same point as the foregoing.

γ. Two arteries to the iris.

δ. The Art. hyaloidea, the terminal portion of the ophthalmic artery. (For further description of these vessels, see Eye.)].

*2.* The *systemic arch* (Ductus aorticus), (Figs. 132, 143, and 145 II) is the middle arch of the three; it arises from the middle canal of the Ductus arteriosus, and winds obliquely round the oesophagus between the MM. petrohyoidei I and II towards the vertebral column, which it reaches at about the level of the sixth vertebra. The right systemic arch is continued as the dorsal aorta, the left arch communicates with it merely by a small opening, and is then continued as the coeliaco-mesenteric artery.

Branches of the systemic arch:--

*a.* The *laryngeal artery* (Arteria laryngea), (Fig. 146 lg) arises from the inner border of the systemic arch before it reaches the oesophagus; it passes forwards and inwards to be distributed in the larynx and pharynx. According to Brücke this artery possesses a valve at its point of origin.

Transverse section at level of the larynx.

C Carotid gland. G Glottis. lg Laryngeal artery. S Subclavian artery. I Carotid arch. II Aortic arch. ]

*b.* The *oesophageal arteries* (Arteriae oesophageae) pass from the upper part of the arch to the dorsal surface of the oesophagus.

*c.* The *occipito-vertebral artery* (Ecker), (Art. occipito-vertebralis), (Fig. 147 o, v) [arises from the systemic arch immediately in front of the transverse process of the second vertebra, and ascends immediately in contact with the body of the first vertebra, which it separates from the MM. intertransversarii capitis and the sympathetic cord]. Immediately under the most anterior portion of the M. longissimus dorsi the artery divides into two branches, the vertebral and occipital arteries:--

(1) The *vertebral artery* (Arteria vertebralis or supra-vertebralis) (Fig. 147 v) courses backwards lying on the transverse processes of the vertebrae and on the MM. intertransversarii, under cover of the M. longissimus dorsi. In this course it is close to the oblique processes, and may even be partially covered by these; it extends beyond the sacrum, and gives off:--

α. The Rami spinales, which pass through the intervertebral foramina to the spinal cord (see Arteries of Spinal Cord, p. 162).

Dissection to show the occipito-vertebral and the cutaneous arteries.

The skin of the back has been divided by a median incision and drawn to either side; the right arm dislocated and removed through the opening in the skin (at A). On the left side the extensor muscles of the back have been removed.

c.m. Cutaneous artery. c.p. Arteria cutanea pectoris. o Occipital artery. s Scapular artery. v Vertebral artery. ]

β. The Rami dorsales; these supply the muscles of the back and send branches to the skin, which accompany the cutaneous branches of the spinal nerves through the Saccus lymphaticus cranio-dorsalis.

γ. The Rami intercostales are distributed in part to the MM. intertransversarii; other twigs pass ventrally to the periganglionic glands; the longest branches accompany the anterior divisions of the spinal nerves to the muscles and skin of the belly (Fig. 145).

(2) The *occipital artery* (Arteria occipitalis), (Figs. 147 and 148 o), the anterior branch of the occipito-vertebral artery, pierces the M. longissimus dorsi; then courses forwards under cover of the Fascia dorsalis and upon the M. temporalis, and divides, behind the eyeball [at the anterior border of the M. temporalis, Virchow], into two branches:--

α. The Ramus orbito-nasalis (Fig. 148 on) accompanies the ophthalmic nerve along the wall of the cranium, and passes through the sphenethmoid, with the nasal branch of the ophthalmic nerve, to the nose, where it divides into two branches supplying the mucous membrane of the nose. In its course through the orbit the artery supplies branches to the Harderian gland and neighbouring parts, and anastomoses with the ascending branch of the Arteria palatina.

β. The Ramus maxillaris communis (Art. temporalis, Virchow), (Fig. 148 m) runs downwards and outwards along the anterior border of the M. temporalis, and passes under the anterior arm of the squamosal bone to course backwards on the upper jaw. At this point the Ramus maxillaris superior (m′) is given off. The main artery continues its backward course to the tympanic membrane, where it divides into its three terminal branches:--

Branches of the occipito-vertebral and cutaneous arteries in the head; side view. The skin (H) has been reflected downwards.

c.m. Cutaneous artery. l.a. M. levator scapulae. m Art. maxillaris communis. m′ Art. maxillaris superior. m″ Art. maxillaris inferior. o Occipital artery. on Art. orbito-nasalis. p.m. Art. pharyngo-maxillaris. v Vertebral artery. ]

(2) A small ascending branch to the tympanic membrane (Virchow).

(3) A Ramus auricularis (Virchow), which forms a rich anastomosis on the hinder wall of the tympanic cavity, and supplies a twig to the tympanic membrane. This passes from the upper border of the membrane to the point of attachment of the Columella auris (extrastapedial), round which it forms a circular anastomosis. The Ramus auricularis also anastomoses with the cutaneous artery.

Dissection to show the occipito-vertebral and the cutaneous arteries.

The skin of the back has been divided by a median incision and drawn to either side; the right arm dislocated and removed through the opening in the skin (at A). On the left side the extensor muscles of the back have been removed.

c.m. Cutaneous artery. c.p. Arteria cutanea pectoris. o Occipital artery. s Scapular artery. v Vertebral artery. ]

(4) A branch passing inwards to the fat-body, and lying immediately in front of the deltoid muscle (Virchow).

(5) A small branch running on to the inner surface of the angle of the jaw and then forwards (Virchow).

(6) A larger vessel, the Ramus maxillaris inferior (Fig. 148 m″), which arises from the Ramus maxillaris superior under cover of the tympanic membrane, and accompanies the Ramus mandibularis of the trigeminal nerve through the M. masseter, or between this muscle and the M. temporalis to the mandible, and then courses forwards to the chin. A large cutaneous branch is given off half-way along the floor of the mouth. The artery gives off many small twigs to supply the neighbouring structures.]

3. The *pulmo-cutaneous arch* (Ductus pulmo-cutaneus), (Figs. 132 143, and 145 III) is the hindmost (fifth embryonic) of the three persistent arches; it passes upwards and forwards on the oesophagus, and at the level of the carotid gland divides into two branches, the pulmonary artery and the cutaneous artery.

a. The *pulmonary artery* (Arteria pulmonalis) runs backwards to the root of the lung, along the outer surface of which it is continued in a sinuous course. It supplies the lung.

b. The *cutaneous artery* (Arteria cutanea magna), (Fig. 149 c.m.) [passes along the deeper surface of the M. petrohyoideus III until near the prootic bone; in this course it travels forwards, outwards, and upwards, crosses the outer border of the muscles, and appears between the M. levator anguli scapulae and the M. sternocleidomastoideus. At this point the artery curves sharply round to reach the angle of the jaw, the hinder border of the M. depressor maxillae inferioris. The curve so formed and the descending limb are covered by the M. depressor maxillae inferioris. The artery then passes backwards to form a rich anastomosis in the skin almost as far as the posterior end of the trunk. It supplies the following branches:--

(1) The Ramus dorsalis (Virchow) arises immediately in front of the curve of the main artery; it ascends behind the M. temporalis, and passes along the anterior border of the M. depressor maxillae to the skin, where it curves backwards. It supplies small twigs forwards as far as the eyelids.

(2) The Ramus auricularis (Virchow) also arises in front of the curve in the cutaneous artery; sometimes it arises from the Ramus dorsalis. The artery winds around the M. petrohyoideus III near its insertion, and so reaches the posterior wall of the tympanic cavity, where it anastomoses with the R. auricularis of the Ramus maxillaris communis.]

(3) The Arteria pharyngo-maxillaris (Fig. 148 p.m.) is a small branch running forwards and outwards to supply the mucous membrane of the larynx, Eustachian tubes, gums, the lower jaw, and the skin under the mouth. It forms a rich anastomosis with branches of the Ramus maxillaris inferior of the occipital artery, and with others from the pharyngeal branch of the carotid artery; a large branch passes forwards to supply the skin of the throat and floor of the mouth.

(4) The Arteria cutanea pectoris (Fig. 149 c.p.) is distributed to the skin of the breast.

*4.* The *subclavian artery* (Arteria subclavia), (Fig. 150 s). The subclavian artery arises from the systemic arch immediately behind the occipito-vertebral artery at the level of the second or third vertebra. The artery then runs outwards alongside and in front of the brachial nerve, between the M. subscapularis and the M. triceps to the arm, where it is known as the brachial artery; in its course it gives off:--

*a.* The Arteria costo-cervicalis (Fig. 150, 1). This artery arises near the systemic arch, and runs backwards, parallel to the vertebral column, over the brachial nerve, and across the transverse processes of the vertebrae. It is distributed more especially to the M. obliquus internus.

*b.* The Arteria coraco-clavicularis (Fig. 150, 2) arises more externally than the last artery; it accompanies the coraco-clavicular nerve on the dorsal surface of the ventral portion of the shoulder-girdle, and passes between the M. deltoideus and M. subscapularis into the Foramen ovale, where it divides to supply these muscles and the M. pectoralis.

Subclavian artery of the left side.

A Systemic arch. A′ Dorsal aorta. c Arteria cutanea medialis superior. c′ Arteria cutanea medialis inferior. ls M. levator scapulae. o.v Occipito-vertebral artery. p Arteria pectoralis. R Radial artery s Subclavian artery. U Ulnar artery. 1 Arteria costo-cervicalis. 2 Arteria coraco-clavicularis. 3 Arteria scapularis posterior. 4 Arteria scapularis superior. 5 Cutaneous artery. 6 Arteria subscapularis. ]

*c.* The Art. scapularis posterior (Fig. 150, 3), a small branch arising opposite at the tip of the second transverse process and passing backwards over the MM. transverso-scapulares, to which it is distributed.

Arteries of the palmar surface of the hand.

B Ulnar artery. ci R. cutaneus medialis inferior. d Digital branches. F M. flexor digitorum communis. II Thumb. V Fifth finger. ]

Arteries of the dorsal surface of the hand.

B Ulnar artery. cri R. cutan. rad. inferior. R Radial artery. II Thumb. V Fifth finger. ]

*d.* The Art. scapularis superior (Fig. 150, 4) accompanies several nerves between the M. subscapularis, M. transverso-scapularis major, and the long head of the M. triceps towards the dorsal surface, where it is distributed to the MM. infraspinatus, latissimus dorsi, etc.

*e.* The Ramus cutaneus maxillaris.

*f.* The Art. subscapularis (Fig. 150, 6) is distributed in the subscapular muscle.

A. The *brachial artery* (Arteria brachialis), (Fig. 150) accompanies the brachial nerve under cover of the long head of the M. triceps and over its inner head to the Plica cubiti, into which it sinks near the tendon of the M. sternoradialis; beyond this point it is continued as the ulnar artery. In its course the brachial artery gives off:--

*a.* The Arteria pectoralis (Fig. 150 p).

*b.* The Arteria cutanea medialis superior (Fig. 150 c).

*c.* The *radial artery* (Arteria radialis), (Fig. 150 R) which winds round the humerus with the radial nerve between the muscles of the outer side of the forearm, to which it gives branches: in the palm of the hand it passes between the M. extensor carpi ulnaris and the M. flexor antibrachii to the dorsal surface of the hand, where it anastomoses with the ulnar artery. In its course it supplies:--

(1) Muscular branches to the surrounding muscles.

(2) The Ram. cut. radialis inferior, which arises from the radial artery towards the distal end of the forearm, and passes underneath the M. flexor carpi ulnaris to the skin.

B. The *ulnar artery* (Arteria ulnaris), (Figs. 150 U, 151 B) accompanies the ulnar nerve towards the hand, passes between the M. flexor digitorum communis and the M. anconeus to the palm of the hand, and then winds round the outer side to the dorsal surface of the carpus to form its terminal branches. The branches are:--

(1) The Ram. cutan. med. inferior (Fig. 151 ci); it arises near the wrist-joint and supplies (α) twigs to the skin of the inner surface; (β) a branch downwards, which courses along the inner side of the second finger to its tip; and (γ) a branch which passes upwards to anastomose with the R. cutaneus medialis superior.

(2) In the palm of the hand a branch (Fig. 151 d) is given off, which divides to form Arteriae digitales volares: one for the second finger, two for the third finger, two for the fourth finger, and one for the fifth finger.

(3) Given off on the dorsum of the hand (Fig. 152) it supplies branches corresponding exactly with those of the palmar surface.

*5.* The *dorsal aorta* (Aorta communis s. abdominalis) (Fig. 153 A). The two systemic arches unite at about the level of the sixth vertebra to form the dorsal aorta: as already mentioned the union is very incomplete, the dorsal aorta being practically a continuation of the right systemic arch, and only communicating with the left by means of a small opening. The branches are as follows:--

*a.* The *coeliaco-mesenteric artery* (Arteria intestinalis communis), (Fig. 153), the true continuation of the left systemic arch, at once divides to form the gastric and mesenteric arteries.

(1) The *gastric artery* (Arteria gastrica s. coeliaca) (c) immediately divides into two branches:--

α. The Ramus dexter s. anterior; this artery gives off the Arteria hepatica to the liver and gall-bladder and passes to the right (anterior) surface of the stomach, running along the attachment of the mesentery and supplying branches forwards to the oesophagus and backwards towards the intestine.

β. The Ramus sinister s. posterior passes to the left (posterior) surface and behaves like the Ram. dexter.

(2) The *mesenteric artery* (Arteria mesenterica superior and inferior, and the Arteria splenica), (Fig. 153 m) supplies:--

α. The superior mesenteric artery, which supplies the upper part of the intestine, and gives off a recurrent branch to the stomach, which anastomoses with the gastric arteries.

Arterial system of Rana esculenta.

A Dorsal aorta. Ad Right systemic arch. As Left systemic arch. c (opposite fore-limb) Carotid artery. c (in abdomen) Coeliac artery. cm Cutaneous artery. e Lingual artery. H Heart. H′ Harderian gland. L Liver. Lu Lung. m Mesenteric artery. M Stomach. M′ Spleen. o Ophthalmic artery. p Pharyngeal artery. p′ Anterior palatine artery. S Subclavian artery. I Carotid arch. II Systemic arch. III Pulmo-cutaneous arch. ]

β. The splenic artery to the spleen.

γ. The inferior mesenteric artery to the lower part of the intestine.

All the arteries to the intestine course in lymph-spaces.

*b.* The *urinogenital arteries* (Arteriae urino-genitales), (Fig. 154 ug) are four to six small arteries arising from the ventral surface of the aorta between the kidneys: they immediately divide into right and left branches to supply the kidneys, fat-bodies, reproductive organs, and their ducts (see kidney).

*c.* The *lumbar arteries* (Arteriae lumbales), are small paired vessels to the neighbouring muscles, and send branches through the intervertebral foramina to the vertebral canal. Sometimes these arteries arise from the Art. spinalis or Art. vertebralis, etc.; in the former case they pass outwards from the vertebral canal to the surrounding structures.

*d.* The *haemorrhoidal artery* (Art. mesenterica inf. s Art. haemorrhoidalis superior) is a small median artery running from the posterior end of the aorta to the large intestine.

*6.* *Bifurcation of the aorta.* *The iliac arteries* (Arteriae iliacae communes). Opposite the middle of the urostyle the aorta bifurcates to form the iliac arteries; each of these courses on the corresponding sciatic plexus to the thigh, beyond which it is continued as the sciatic artery. The branches of the iliac artery are:--

*a.* The *vesico-epigastric artery* (Arteria epigastrico-vesicalis), (Fig. 155 ev); it arises near the bifurcation, passes outwards on the plexus, and divides into two branches:--

(1) The epigastric artery (Arteria epigastrica) (e) immediately gives off a recurrent branch to the iliac bone and the M. ilio-coccygeus; it then continues to the ventral muscles of the abdominal wall, where it runs forwards on the deeper surface of the M. obliquus internus, and is distributed more especially to this muscle.

The urinogenital arteries.

A Dorsal aorta. H Testis. N Kidney. ug Urinogenital arteries. ]

(2) The hypogastric artery (Arteria vesicalis) (v) winds downwards around the sciatic plexus to reach the mesentery, along which it courses to the bladder, where it forms a rich anastomosis.

*b.* The *femoral artery* (Arteria femoralis s. cruralis), (Fig. 155 f) is the representative of the femoral artery of man, although it does not perform the same functions. The artery passes under the hinder free border of the M. obliquus internus to the thigh, where it lies upon the M. ilio-psoas, and sends twigs to the neighbouring muscles, the skin, and lymph-sac (Lamina inguinalis), and then divides into:--

(1) A twig, which runs forwards on the ventral surface of the iliac bone and is covered by the epigastric artery.

(2) A twig, running forwards and downwards on the MM. ilio-psoas, vastus internus, and sartorius, to send branches to the hip-joint.

*c.* The *spermatic artery* (Arteria spermatica), which arises, in males, from the iliac artery, and ascends to the Vesicula seminalis.

Bifurcation of the aorta and the iliac arteries.

e Epigastric artery. ev Vesico-epigastric artery. f Femoral artery. o Internal oblique muscle. v Vesical artery. ]

*7.* *Arteries of the hinder extremity.*

A. The *sciatic artery* (Arteria ischiadica), (Fig. 156 i) is the continuation of the iliac artery; it leaves the pelvis between the hinder (outer) border of the M. coccygeo-iliacus and the inner surface of the origin of the M. ilio-psoas, then lies between the former muscle and the origin of the M. vastus externus. It appears on the thigh between the M. vastus externus (in front) and the M. pyriformis (behind); it is the main arterial trunk for the hinder extremity. The artery courses backwards, lying upon the sciatic nerve and between the M. biceps and the M. semimembranosus; in this course it runs in a lymph-space placed in the Septum femorale superius (see page 259). Arrived at the popliteal space the artery bifurcates to form the peroneal and tibial arteries; near the pelvis it gives off two branches (*a*) and (*b*), and in its course along the thigh two branches (*c*) and (*d*).

*a.* The Art. haemorrhoidalis inferior (h) runs backwards and inwards under the M. pyriformis to be distributed in the M. sphincter ani and the skin of the anus.

*b.* The Art. cutanea femoris posterior v. superior (cf′) runs with the corresponding nerve and the M. pyriformis, and over the M. semimembranosus to the skin of the inner and hinder surfaces of the thigh.

*c.* The Rami musculares supply the M. semimembranosus, the M. biceps, and the MM. extensores auris; the branch to the M. rectus inferior major pierces the muscle in company with the nerve, and is continued as:--

*d.* The Art. cutanea femoris media (cf″) to the skin of the middle of the inner surface of the thigh. Several small twigs pierce the M. rectus internus minor, reach the skin, and communicate with this artery.

Arteries of the hinder extremity.

cc Art. cutanea calcanei. cf Cutaneous branch of the femoral artery. cf′ Art. cutanea fem. post. superior. cf″ Art. cutanea femoris media. cgl Art cut. genu lateralis superior. cgl′ Art. circumflexa genu lateralis inferior. cgm Art. circumflexa genu superior medialis. cgm′ Art. circumflexa genu inferior medialis. ci M. coccygeo-iliacus. g M. gastrocnemius. gl M. glutaeus. h Art. haemorrhoidalis inferior. i Sciatic artery. ml Art. malleolaris lateralis. mm Art. malleolaris medialis. p Art. peronea. p′ Muscular branch to the M. peroneus. P M. pyramidalis. ra M. rectus anterior. ri″ M. rectus internus. sm M. semimembranosus. su Art. suralis. t Tibial artery. to Aperture in tibio-fibula. tr Art. tarsea. ve M. vastus externus. ]

B. The *peroneal artery* (Art. peronea), (Fig. 156 p) runs outwards under cover of the tendon of the M. biceps femoris, and accompanies the peroneal nerve downwards to give off:--

*a.* The Art. circumflexa genu lateralis superior, which runs forwards on the outer side of the knee, gives a twig to the joint, and is continued as:--

*b.* The Art. cutanea genu lateralis superior (cgl) to the skin of the anterior and outer sides of the knee. It anastomoses with branches of the Arteriae circumflexae genu mediales to form a rich anastomosis (Rete articulare genu): other branches pass upwards to inosculate with the Art. cutanea femoris anterior (cf), and others downwards to anastomose with the next artery.

*c.* The Art. circumflexa genu lateralis inferior (cgl′) runs under the tendon of origin of the gastrocnemius to the outer side of the knee, and terminates in the skin as the Art. cutanea genu lateralis inferior. Some of the cutaneous twigs pass upwards to anastomose with the Art. cut. genu lat. superior, others downwards to anastomose with the AA. malleolares.

*d.* A muscular branch (p′) for the M. peroneus; it is the real continuation of the peroneal artery, and runs behind the outer tendon of origin of the gastrocnemius to be distributed in the M. peroneus.

C. The *tibial artery* (Arteria tibialis), (Fig. 156 t), arises at the bifurcation of the sciatic, and runs inwards, meeting the tibial nerve between the tendons of origin of the M. gastrocnemius, and deep in the popliteal space under cover of the calf-muscles. It then pierces the M. tibialis posticus, and leaves this to perforate the tibio-fibula (see p. 50), appearing again on the anterior surface as the anterior tibial artery. Before meeting the tibial nerve this artery gives off the following branches:--

*a.* The Art. circumflexa genu superior medialis (cgm), which winds round to the front of the knee-joint, and gives off a cutaneous branch, the Art. cutanea genu medialis superior, which is distributed in the skin of the inner side of the knee and anastomoses above with the Art. cutanea femoris media, below with the following branches (*b*, *c*, and *d*).

*b.* The Art. circumflexa genu inferior medialis (cgm′) supplies twigs to the knee-joint, and passes to the skin of the knee and inner surface of the calf as the Art. cutanea inferior medialis.

*c.* Muscular twigs to the M. gastrocnemius.

*d.* The Art. suralis (su); this accompanies the N. suralis downwards along the calf-muscle, and is distributed in the skin of the inner side of the heel.

*e.* While passing between the fibres of the M. tibialis posticus, the tibial artery gives off muscular twigs; one larger than the rest is known as the Ramus descendens.

D. The *anterior tibial artery* (Arteria tibialis antica), (Fig. 157 t.a.) is the continuation of the tibial artery after piercing the tibio-fibula. It runs downwards on the anterior surface of the leg, then between the two heads of the M. tibialis anticus to the dorsum of the foot, where it is continued as the Arteria dorsalis pedis. It supplies:--

Arteries of the dorsal surface of the foot.

c.c. Art. cutanea calcanei. c.c.i. Art. cutanea cruris inferior. Ft′ M. flexor tarsi. h Art. cutanea hallucis. i1 Art. interossea dorsalis I. i2 Art. interossea dorsalis II. i3 Art. interossea dorsalis III. i4 Art. interossea dorsalis IV. ml Art. malleolaris lateralis. m.m. Art. malleolaris medialis. t.a. Anterior tibial artery. ta* Bifurcation of the dorsalis pedis artery. tr Art. tarsea. ]

*a.* Rami musculares to the M. peroneus, M. extensor cruris, and to the M. flexor tarsi anterior.

*b.* The Art. cutanea cruris inferior (c.c.i.) passes between the two heads of the M. tibialis anticus to the skin of the anterior and outer sides of the leg.

*c.* The Art. cutanea calcanei (c.c.) is given off at the ankle-joint; it runs outwards on the lower end of the tibio-fibula, giving branches to the joint, then backwards between the tibio-fibula and the M. peroneus to be distributed to the skin of the heel. Above it anastomoses with the A. circumflexa genu inf. lateralis, and below with the malleolar arteries.

*d.* The Art. malleolaris lateralis (ml) arises a little beyond the last artery; it runs outwards under the origin of the M. flexor tarsi, gives branches to the joint and muscles, and terminates in the skin of the outer border and dorsal surface of the foot.

*e.* The Art. malleolaris medialis (m.m.) arises at about the same level as the Art. malleolaris lat. from the inner border of the anterior tibial artery. It supplies branches to the joint, gives numerous branches to the skin, which anastomose with the Art. suralis, and passes to the inner border of the foot, where it ends by distributing branches to the M. plantaris, the extensor aponeurosis, and, as the Art. cutanea plantaris, to the skin of the sole of the foot.

E. The *dorsal artery* of the foot (Art. dorsalis pedis), (Fig. 157 t.a.) runs under the M. flexor tarsi posterior to the point ta*, where it is superficial; the artery then bifurcates; the branches are:--

Arteries of the sole of the foot.

i Art. interossea. pf Rami perforantes. ]

*a.* The Art. tarsea (tr) which arises from the dorsal artery of the foot while under cover of the M. flexor tarsi posterior; it passes to the M. extensor digiti V and to the skin of the dorsum and outer border of the foot. One branch courses along the outer border of the fifth toe to its tip; another passes upwards to anastomose with the neighbouring vessels.

*b.* The inner branch, formed by the bifurcation of the dorsal artery of the foot, at once divides to form:--

(1) The Art. cutanea hallucis (h) to the supplemental great toe.

(2) The Art. interossea dorsalis I (i^1), which at once bifurcates to form two Rami digitales for the first and second toes; these inosculate with the Art. cutanea plantaris, and send twigs to the skin of the inner border of the foot.

*c.* The outer branch formed by the bifurcation of the dorsal artery divides to form the Arteriae interossei dorsales II, III, and IV (i^2, i^3, i^4); they are distributed in a rich anastomosis to the web.

*d.* The Arteria interossea (Fig. 158 i) arises from the dorsal artery of the foot at the tarsus, and perforates the membrane between the astragalus and calcaneum to reach the sole of the foot. It forms a rich subcutaneous plexus on the calcar, and anastomoses with the Rami perforantes (Fig. 158 pf), which pass above the upper borders of the Musculi interossei to reach the plantar surface, where they give off small Rami interossei volares to anastomose with the AA. interosseae dorsales.

III. THE VEINS.

(The arrangement of this section has been modified.)

The blood, distributed to the body by means of the arteries, is returned to the heart by the veins, which conduct the blood directly or indirectly to the auricles. The pulmonary vein opens directly into the left ventricle, the three Venae cavae open into the Sinus venosus.

A. *Vein opening into the left auricle.*

The *pulmonary vein* (Vena pulmonalis communis), (Fig. 159 vp). The blood returning from each lung is gathered into a vessel lying along the inner side of the root of the lung. That of the right side is somewhat longer than the left; the two vessels (Venae pulmonales dextra et sinistra) run above the corresponding anterior caval veins to form a common trunk, the pulmonary vein, which opens into the left auricle (see p. 215).

B. *Veins opening into the* Sinus venosus.

The veins opening into the Sinus venosus are the three caval veins; of these the two anterior open into the anterior angles of the Sinus venosus, the posterior into the posterior angle.

*1.* The *Anterior Caval Veins* (Vena cava superior), (Figs. 133 V, 159 C a) are a pair of large veins opening into the Sinus venosus and returning to it blood from the fore-limbs and sides of the head. Each vein is formed by the union of a small vein, the external jugular, with two large veins, the innominate and the subclavian veins.

*a.* The *external jugular vein* (Vena jugularis externa), (Fig. 159 je) is formed, at the outer border of the hyoid bone, by the union of two veins:--

(1) The lingual vein (Vena lingualis) (Fig. 161 l). This originates at the tip of the tongue and passes in a very tortuous course along the ventral surface of the hyoid; it receives numerous branches from the tongue and hyoid muscles.

(2) The mandibular vein (Vena maxillaris inferior), (Fig. 161 m) runs along the insertion of the M. submaxillaris, and turns inwards at its hinder border to join the lingual vein.

*b.* The *innominate vein* (Vena anonyma), (Fig. 160 A) is formed by the union of the internal jugular and the subscapular veins. By tracing the innominate vein upwards between the suspensorium and the shoulder-girdle, the internal jugular vein will be seen to receive the vertebral vein at the outer border of the M. levator scapulae. The left innominate vein receives the Vena bulbi anterior from the Truncus arteriosus (p. 222).

Schema of the veins of Rana esculenta.

a Subclavian vein. ab Anterior abdominal vein. Ad Right auricle. As Left auricle. Ca Anterior vena cava. Cp Posterior vena cava. cm Cutaneous vein. d Vena dorso-lumbalis. D Intestine. f Femoral vein. i Sciatic vein. ic Vena communicans iliaca. je External jugular vein formed by lingual and maxillary veins l and m. ji Internal jugular vein. L Hepatic veins. N Kidney. o Oviducal veins. P Hepatic portal vein. raI Renal portal vein. raII Secondary renal portal veins. re Renal veins. s Subscapular vein. SC Sinus venosus. va Innominate vein. vc Vena bulbi posterior (cardiac vein). vp Pulmonary veins. ]

(1) The *internal jugular vein* (Vena jugularis), (Fig. 160 J) can be traced from the border of the M. levator scapulae upwards and forwards to the hinder part of the prootic bone: it then passes forwards under the lateral process of the prootic, in a groove on the anterior surface of the same bone, towards the hinder angle of the orbit, where it receives the veins from the cranial cavity (see vessels of brain, p. 165), and also a branch from the orbit.

Distribution of the internal jugular vein and the anterior portion of the cutaneous vein.

A Innominate vein. c.m. Cutaneous vein. f Nasal vein. h Harderian gland. H Skin, reflected downwards. J Internal jugular vein. L Anterior lymph-heart. l M. levator scapulae. O M. obliquus internus. o Vena orbitalis anterior. o′ Vena orbitalis posterior. P Lateral process of the prootic bone. S Subscapular vein. S′ Shoulder-girdle. T Tympanic membrane. V Vertebral vein. 2 Transverse process of the second vertebra. 3 Transverse process of the third vertebra. 4 Transverse process of the fourth vertebra. ]

α. [The Vena orbitalis media (Virchow); it arises from the anterior internal angle of the orbit, from the Harderian gland, the nasal cavity, or from other veins on the anterior wall of the orbit. The vessel lies close to the cranium, immediately underneath the Arteria nasalis, and sinks under the M. rectus superior to join the internal jugular vein. In its course it receives the Vena bulbi superior (see eye), and near its termination communicates with the Vena orbitalis posterior.]

β. The Vena vertebralis (Fig. 160 V) arises posteriorly and runs forwards over the transverse processes of the vertebrae, the Musculi intertransversarii, and the M. levat. scapulae, to join the internal jugular vein. In its course it receives branches (Venae spinales) from the vertebral canal through the intervertebral foramina, and cutaneous branches which accompany the corresponding arteries and nerves through the dorsal lymphatic sac. The vein pulsates in consequence of its connection with the anterior lymph-heart (Müller).

(2) The *subscapular vein* (Vena subscapularis), (Fig. 160 S). This vein arises in the transverse abdominal muscles and the muscles of the shoulder girdle; it unites with the internal jugular vein under the shoulder-girdle.

*c.* The *subclavian vein* (Vena subclavia), (Fig. 159) passes backwards from the anterior caval vein on the dorsal surface of the coracoid bone and the clavicle, and then under cover of the Portio sternalis of the M. pectoralis major, to the internal border of the Portio abdominalis of the M. pectoralis major, where it is formed by the union of the cutaneous vein and the brachial vein.

The anterior caval vein and its branches.

a Innominate vein. c.m. Cutaneous vein. c.s. Anterior cava vein. i Internal jugular vein. i′ External jugular vein. l Lingual vein. m Mandibular vein. s Brachial vein. s.c. Subscapular vein. ]

(1) The cutaneous vein (Vena cutanea magna, Ecker; Vena musculo-cutanea, Gruby), (Figs. 160, 161, and 162 c.m.). This vein arises by small branches in the head; these are:--

α. The Vena nasalis (Virchow); it arises by an upper and a lower branch from around the nostril, and courses backwards along the superior maxillary bone to about the middle of the orbit, where it joins the facial vein.

β. The Vena orbitalis anterior (Virchow), (Vena ophthalmica anterior, Ecker), (Fig. 160 o) commences at the Harderian gland from a rich anastomosis, receives branches from the floor and anterior wall of the orbit, and joins the facial vein with the Vena nasalis.

Course of the cutaneous vein as seen from the side.

c.m. Cutaneous vein. d M. depressor maxillae. i M. infraspinatus. ]

γ. The Vena orbitalis posterior (Virchow), (Vena ophthalmica posterior, Ecker), (Fig. 160 o′) arises on the posterior wall of the orbit on the M. pterygoideus; it passes under the Processus zygomaticus to join the facial vein, and in its course receives the Vena ophthalmica (see eye), and communicates with the Vena orbitalis medialis and the internal jugular vein.

δ. The Vena facialis (Fig. 160) is formed about the middle of the orbit by the union of the Vena nasalis and the Vena orbitalis anterior; it courses backwards towards the angle of the jaw. On reaching the M. depressor maxillae, about 4 mm. in front of the angle of the jaw, it passes on to the skin. It receives in its course the Venae palpebrales (Fig. 162) and the Vena orbitalis posterior.

The musculo-cutaneous vein is the direct continuation of the Vena facialis after this has left the upper jaw; it immediately receives one or more twigs (Venae tympanicae), (Fig. 162) from the tympanic membrane and the tympanic cavity.

The vein then courses backwards in the outer wall of the lateral lymph-sac as far as the middle of the trunk, where it passes, by means of the Septum abdominale, to the outer border of the Portio abdominalis of the M. pectoralis; here the vein curves round to pass forwards between the fibres of this muscle to its inner border where it terminates by joining the brachial vein. In the whole of this lengthy course the vein receives numerous branches from the neighbouring parts.

Veins in the region of the kidney.

a Renal portal vein. a′ Dorso-lumbar veins. abd Anterior abdominal vein. d Intestine. f Femoral vein. i Sciatic vein. N Kidney. o Right ovary, drawn to the left. o′ Oviduct. ov Oviducal veins. p Mesenteric veins. r Renal veins. V Bladder. v.c.i. Posterior vena cava. Vv Vesical veins. ]

(2) The *brachial vein* (Vena brachialis) is formed in the Plica cubiti by the union of two veins.

α. The *radial vein* (Vena radialis) arises on the dorsum of the hand from a venous arch, the distal convexity of which receives the Venae digitales dorsales: the vein courses superficially along the outer side of the forearm to the elbow.

β. The *ulnar vein* (Vena ulnaris) arises from the veins in the palm of the hand, and courses towards the elbow, lying deeply between the muscles of the inner and outer surfaces of the forearm. In the elbow the vein becomes superficial near the tendon of the M. sterno-cleidoradialis, and joins the radial vein to form the brachial vein.

The cutaneous veins of the fore-limb follow courses corresponding with those of the arteries.

*2.* The *Posterior Caval Vein* (Vena cava inferior), (Fig. 159 Cp, 163 v.c.i.). The posterior caval vein is a median vein which, commencing between the kidneys, runs forwards to open into the posterior end of the Sinus venosus. It receives the hepatic, renal, and ovarian or spermatic veins.

*a.* The hepatic veins (Venae hepaticae), (Fig. 164 v.h.) are two in number, one from either side of the liver; they open into the posterior caval vein near the Sinus venosus.

*b.* The *renal veins* (Venae renales or Venae revehentes), (Fig. 163 r) are four or five small vessels on each side; they pass from the inner border of the kidney inwards and forwards, to form, by their union, the posterior caval vein. The most anterior receive branches from the fat-bodies (see kidney).

*c.* The *spermatic* or *ovarian veins* are four or five in number on each side; they open into the posterior caval vein between the renal veins.

*3.* The *Portal Systems*.

The femoral vein on entering the pelvis divides to form two branches; an iliac vein placed dorsally, and a pelvic vein placed ventrally; the two pelvic veins converge to the middle line of ventral wall of the abdomen, where they unite to form the anterior abdominal vein.]

*a.* The *renal portal vein* (Vena renalis advehens princeps), (Fig. 163 a). This vein is formed by the union of the sciatic and the iliac veins; it courses forwards to the outer border of the kidney, and is distributed, by numerous branches, to that organ, chiefly on its dorsal surface. It receives the following veins:--

(1) The *iliac vein* (Vena iliaca externa); this is the dorsal branch formed by the bifurcation of the femoral vein.

(2) The *sciatic vein* (Vena ischiadica), (Figs. 163 and 165 i) arises at the popliteal space, courses upwards in company with the sciatic nerve between the M. semitendinosus and the M. biceps, then passes, still with the nerve, between the M. vastus externus and the M. pyramidalis into the pelvis. It continues forwards to join the iliac vein. At the root of the thigh this vein communicates with the femoral vein by the Ramus communicans iliacus.

(3) The *dorso-lumbar vein* (Vena dorso-lumbalis), (Fig. 163 a′) is a vein (or more usually several) arising by twigs in the dorsal and outer walls of the abdomen; it joins the renal portal vein opposite the kidney.

(4) The *oviducal veins* (Fig. 163 ov) are irregular veins from the oviducts, which open either into the dorso-lumbar vein, or into the renal portal vein.

*b.* The *hepatic portal system*.

The liver receives blood from two sources: (1) from the hind-limbs by means of the anterior abdominal vein, and (2) from the alimentary canal by the hepatic portal vein.

Veins of the liver.

AA Auricles. aa Right and left branches of anterior abdominal vein. b Ramus descendens. c Vena bulbi (Vena cardiaca). D Intestine. G Gall-bladder. L.l. Left lobe of liver. L.r. Right lobe of liver. P Hepatic portal vein. P′ Intestinal veins. P″ Gastric veins. S Sinus venosus. V Ventricle. Va Anterior abdominal vein. V.c.i. Posterior vena cava. v.h. Hepatic veins. ]

The *anterior abdominal vein* (Vena abdominalis), (Figs. 159 ab, 164 Va) is formed, a little in front of the symphysis pubis, by the union of the two pelvic veins. It courses forwards along the middle line of the ventral body-wall until opposite the liver, where it ascends and divides into three branches, of which two enter the right and left lobes of the liver respectively. The third, the Ramus descendens, joins the hepatic portal vein. The anterior abdominal vein receives the following veins:--

α. The vesical vein (Vena vesicalis), (Fig. 163 Vv); a median vein arising in the groove between the lobes of the bladder from lateral branches, which extend outwards on the bladder. This vein communicates above with other vesical twigs which open into the haemorrhoidal vein.

β. Parietal veins, which join the anterior abdominal vein in its course along the ventral body-wall.

γ. A cardiac vein (Vena cardiaca), (Figs. 142, 159 vc, 164 c), which joins the anterior abdominal vein just before its division (see p. 222).

The *hepatic portal vein* (Vena portarum), (Figs. 159, 164 P) is formed by the union of the gastric, intestinal, splenic, and one of the haemorrhoidal veins. The large vein so constituted passes forwards towards the liver, receives the Ramus descendens from the anterior abdominal vein, and then passes into the left lobe of the liver. Its branches are the following:--

(1) The *gastric veins*. The stomach has three veins:--

α. [The Vena coronaria ventriculi, which receives blood from the hinder end of the oesophagus and anterior portion of the stomach.

β and γ. Two other veins which form an Arcus coronarius on the concave surface of the stomach; the hinder receiving in addition the small Venae pancreaticae and the Vena duodenalis; the trunk so formed receives the Vena coronaria ventriculi (Hoffmann).

(2) The *intestinal veins*; the veins of that portion of the alimentary canal between the middle of the duodenum and the anterior end of the large intestine open into a common vein which joins the hepatic portal vein.

(3) The *splenic vein* joins either the hepatic portal vein or one of the intestinal veins.

(4) The *haemorrhoidal veins* are three in number; the anterior opens into the splenic vein, the remaining two into the portal veins through the agency of the intestinal veins.]

*4.* *The Veins of the Hinder Extremity.*

The hinder extremity has two venous trunks, the sciatic vein and the femoral vein.

*a.* The *femoral vein* (Vena femoralis), (Fig. 165 f) is the larger venous trunk of the hinder extremity. It arises in the popliteal space as a direct continuation of the posterior tibial vein, courses upwards in company with the sciatic artery and nerve, then leaves these to wind forwards and outwards, and appears between the origins of the M. vastus externus and of the M. rectus anterior. The vein here gives off the Ramus communicans iliacus to the sciatic vein, and turns forwards and downwards around the M. glutaeus maximus to reach the floor of the pelvis, near the femoral artery. The vein then bifurcates to form the pelvic and iliac veins.

Veins of the hinder extremity, half schematic.

c.i. Vena communicans iliaca. f Femoral vein. i Sciatic vein. i′ Vena cutanea cruris medialis. r.a. M. rectus anterior. s.m. M. semimembranosus. v.e. M. vastus externus. ]

(1) The Ramus communicans iliacus (Fig. 165 c.i.) forms a communication with the sciatic at the base of the thigh.

(2) The posterior tibial vein (Vena tibialis postica), of which the femoral is a continuation, arises on the dorsal surface of the toes and foot. It runs superficially on the M. extensor longus digiti primi over the ankle-joint, courses upwards and winds round the outer surface of the tibio-fibula to the flexor surface. It receives, in its course, muscular branches, and at the knee a large cutaneous branch.

*b.* The *sciatic vein*: this vein has already been described (see p. 247), but the vein from which it arises requires description.

The *anterior tibial* vein (Vena tibialis antica) arises on the dorsum of the foot by twigs from the toes; it courses under the M. extensor longus digiti primi, then upwards on the anterior surface of the leg, and enters the canal in the tibio-fibula to appear on its hinder surface. The vein then receives twigs from the M. peroneus, the M. tibialis posticus, the M. gastrocnemius, and a large cutaneous branch.

α. The Vena cutanea cruris medialis (Fig. 165 i′) receives branches from both above and below, and enters the popliteal space to join the anterior tibial vein.

β. The anastomosis on the dorsum of the foot, from which the anterior tibial vein arises, receives perforating twigs from the plantar surface.