Part 178

FIG. 461.—SUPERFICIAL VESSELS AND NERVES OF HEAD AND ANTERIOR PART OF NECK OF HORSE.

a, Masseter; b, parotid gland; c, parotido-auricularis; 1, masseteric artery; 2, parotid branch; 3, transverse facial artery; 4, facial artery; 5, 6, inferior labial artery; 7, superior labial artery; 8, lateral nasal artery; 9, infraorbital artery; 10, dorsal nasal artery; 11, angular artery of eye; 12, 13, jugular vein; 14, great auricular vein; 15, masseteric vein; 16, superficial temporal vein; 17, transverse facial vein; 17′, deep temporal vein; 18, external maxillary vein; 19, facial vein; 20, labial vein; 21, dorsal nasal vein; 22, lateral nasal vein; 23, angular vein of eye; 24, 25, facial nerve; 25′, 25″, superior and inferior buccal nerves; 26, transverse facial nerve; 27, auriculo-palpebral nerve; 28, anterior auricular nerve; 29, cervical branch of facial nerve; 30, ventral branch of second cervical nerve; 30′, 30″, 30‴, auricular and cutaneous branches of 30; 31, branches of dorsal division of first and second cervical nerves; 32, dorsal branch of spinal accessory nerve. (After Leisering’s Atlas.) ]

4. The =great auricular vein= (V. auricularis magna) is a satellite of the posterior auricular artery above, but joins the jugular a variable distance below and behind the point of origin of the artery.

5. The =inferior cerebral vein= (V. cerebralis ventralis) is an emissary of the cavernous sinus of the dura. It is a satellite of the internal carotid artery, receives the =condyloid vein=, and joins the jugular near the occipital vein or by a common trunk with it.

6. The =occipital vein= (V. occipitalis) arises in the fossa atlantis by the union of muscular and cerebrospinal branches. The former comes from the muscles of the poll and passes through the foramen transversarium. The latter is connected with the occipital sinus of the dura mater and emerges from the spinal canal by the intervertebral foramen.

7. The =external maxillary= or =facial vein= (V. maxillaris externa) arises by radicles which correspond in general to the branches of the artery of like name. It passes down over the cheek along the anterior border of the masseter muscle behind the artery, crossing over the parotid duct, which lies behind the vein lower down. Thus on the ramus and as they turn around its lower border the artery is in front, the vein in the middle, and the duct posterior. In the submaxillary space the vein is ventral to the artery for some distance, then parts company with the artery, runs straight backward along the lower border of the parotid gland, and opens into the jugular vein at the posterior angle of the gland. The chief differences in the tributaries of the vein as compared with the branches of the corresponding artery are as follows:

The =labial veins= (Vv. labiales) form a plexus in the submucous tissue of the cheek from which two veins emerge. The upper one passes back and joins the buccinator vein. The lower one (V. labialis communis) joins the external maxillary vein.

Three veins connect with the external maxillary at the anterior border of the masseter.

The upper one is the =transverse facial=, which unites close to the end of the facial crest.

A little lower is the large valveless =vena reflexa= or =alveolar vein=. This passes back under the upper part of the masseter on the maxilla, turns around the tuber maxillare, perforates the periorbita, and joins the ophthalmic vein. It is relatively small at each end, but presents one or two large fusiform dilatations. It receives the following tributaries: (a) The =palatine vein= (V. palatina major), which separates from the palatine artery at the anterior palatine foramen and passes in the groove between the tuber maxillare and the palate bone. The palatine veins form a very rich plexus of valveless vessels in the submucosa of the hard palate, which consists of several layers anteriorly. (b) The =sphenopalatine vein= (V. sphenopalatina) forms a rich plexus of valveless vessels on the turbinal bones and the septum nasi. It is usually joined by the =infraorbital vein= (V. infraorbitalis) to form a short common trunk.

FIG. 462.—DISSECTION OF SUBMAXILLARY SPACE AND ADJACENT PART OF NECK OF HORSE.

a, Ramus of mandible; b, sterno-cephalicus muscle; c, c′, omo-hyoidei and sterno-hyoidei (portion removed on right side); d, hyoid bone; e, anterior belly of digastricus; f, g, mylo-hyoideus; h, submaxillary lymph glands (portion removed on right side); i, parotid gland; k, submaxillary gland; l, chin; m, stylo-maxillaris; 1, parotid duct; 2, facial vein; 3, facial artery; 4, external maxillary vein; 5, sublingual vein; 6, sublingual artery; 7, ventral branch of first cervical nerve; 8, mylo-hyoid nerve. (After Ellenberger, in Leisering’s Atlas.) ]

The venous plexuses are remarkably developed in certain parts of the nasal mucosa. On the septum a little below its middle and on the turbinals the veins are in several layers. The olfactory region does not share in this arrangement and the veins here are small and join the ethmoidal vein.

(c) The =ophthalmic vein= (V. ophthalmica) is a short trunk, connected in front with the vena reflexa and behind with the cavernous sinus through the foramen lacerum orbitale. It receives veins which correspond to the arterial branches.

The =buccinator vein= (V. buccinatoria) extends backward from the external maxillary along the lower border of the depressor labii inferioris and buccinator under cover of the masseter, passes between the ramus of the mandible and the tuber maxillare and is continued as the internal maxillary vein. It has a large fusiform dilatation and is valveless. It receives a large common labial vein from the labial plexus, and is usually connected with the masseteric vein.

FIG. 463.—DEEPER VESSELS AND NERVES OF HEAD OF HORSE.

The parotid gland, most of the masseter muscle, and a portion of the ramus of the mandible are removed. a, Remnant of masseter muscle; b, internal pterygoid muscle; c, stylo-mandibularis; d, d′, levator labii superioris proprius (portion removed); e, periorbita; 1, masseteric artery; 1′, parotid branch; 2, trunk for anterior (3) and posterior (4) auricular arteries; 5, 5′, superficial temporal artery; 5″, transverse facial artery; 6, inferior alveolar (or dental) artery; 6′, mental continuation of 6; 7, buccinator artery; 8, infraorbital artery; 9, 11, jugular vein; 10, external maxillary vein; 12, inferior cerebral vein; 13, facial vein; 14, angular vein of eye; 15, dorsal nasal vein; 16, lateral nasal vein; 17, superior labial vein; 18, 19, inferior labial veins; 20, labial plexus; 21, 22, emergent veins of plexus; 23, vena reflexa; 24, trunk of sphenopalatine and infraorbital veins; 25, palatine vein; 26, great auricular vein; 27, 28, superficial temporal vein; 29, transverse facial vein; 30, buccinator vein; 31, dorsal lingual vein; 32, inferior alveolar or dental vein; 33, pterygoid vein; 34, deep temporal vein; 35, superior cerebral vein; 36, external nasal nerve; 37, anterior nasal nerve; 38, superior labial nerve; 39, masseteric nerve; 39′, end branches of 39; 40, buccinator nerve; 41, pterygoid nerve; 41a, inferior alveolar or dental nerve; 41b, mylo-hyoid nerve; 42, posterior auricular nerve; 43, auricular branch of vagus; 44, internal auricular nerve; 45, auriculo-palpebral nerve (cut); 46, digastric nerve. (After Leisering’s Atlas.) ]

The =lingual vein= (V. lingualis) is not a satellite of the artery. It is formed at the side of the lingual process of the hyoid bone by the confluence of several veins which come from the substance of the tongue. One or two considerable vessels run partly in the substance of the hyo-glossus, and another in the genio-hyoideus. The vein is at first covered by the mylo-hyoideus, perforates that muscle, runs back along the omo-hyoideus in relation to the submaxillary lymph glands, and joins the external maxillary near the posterior border of the jaw. Near its termination it receives the =sublingual vein=, or the latter may open into the external maxillary directly.

8. The =thyroid vein= (V. thyreoidea) is a large vessel which joins the jugular near the external maxillary vein. It receives anterior thyroid, laryngeal, and pharyngeal radicles, and sometimes a posterior thyroid vein.

9. =Muscular=, =tracheal=, and =œsophageal= veins.

10. The =cephalic vein= (Vena cephalica) enters the jugular near its termination. It will be described with the veins of the thoracic limb.

11. The =inferior cervical vein= (V. cervicalis ascendens) accompanies the artery. It may open into the brachial vein.

THE SINUSES OF THE DURA MATER

These (Sinus duræ matris) are blood-spaces between the meningeal and periosteal layers of the dura mater and are lined with endothelium. In many places the lumen is crossed by fibrous strands. They receive the veins of the brain, communicate with the meningeal and diploic veins, and with veins outside of the cranium; their connections with the latter are by means of small =emissary veins= (Emissaria). They convey the blood directly or indirectly to the jugular veins. Some are paired, others unpaired. They may be divided into dorsal and basilar systems. The =dorsal system= comprises the following:

The =superior longitudinal= or =sagittal sinus= (S. sagittalis superior) is situated in the upper border of the falx cerebri along the internal sagittal crest. It begins at the crista galli and ends at the tentorium osseum by dividing into two transverse sinuses. It receives the superior cerebral veins. Along each side are small pouches (Lacunæ laterales) into which the veins open. The lumen of the sinus is traversed by fibrous bands and is partially divided by a longitudinal septum.

FIG. 464.—MEDIAN SECTION OF HEAD OF HORSE, UPPER PART WITH SEPTUM NASI REMOVED.

a, Lateral mass of ethmoid bone; b, superior turbinal; c, inferior turbinal; d, d′, turbinal folds; e, frontal sinus; f, falx cerebri; g, tentorium cerebelli; h, medial surface of hemisphere; i, cerebellum; k, occipital bone; k′, occipital condyle; k″, paramastoid process; l, external auditory meatus; m, temporal condyle; n, parieto-temporal canal; 1, branches of ethmoidal artery; 2, 2′, branches of sphenopalatine artery; 3, 3′, branches of sphenopalatine vein; 4, branches of ethmoidal nerve; 5, 5′, branches of sphenopalatine nerve; 6, artery of corpus callosum; 7, superior sagittal sinus; 8, straight sinus; 9, vena magna cerebri; 10, inferior sagittal sinus; 11, 11′, transverse sinuses; 12, superior petrosal sinus; 13, superior occipital sinus; 14, superior cerebral vein; 15, corpus callosum; 16, fornix. (After Ellenberger, in Leisering’s Atlas.) ]

The =transverse sinuses= (S. transversi), right and left, pass outward in the transverse grooves of the parietal bones, enter the parieto-temporal canals, and are continued by the superior cerebral veins to the superficial temporal veins. The two sinuses are connected by the sinus communicans.