Part 167

3. The =vertebral artery= (A. vertebralis) arises from the brachial (or brachiocephalic) opposite the first intercostal space and passes upward and forward. On the left side it crosses the œsophagus, on the right the trachea. Emerging from the thorax it passes between the longus colli internally and the scalenus externally, under the transverse process of the seventh cervical vertebra, and continues along the neck through the series of foramina transversaria, between which it is covered by the intertransversales colli. Emerging from the foramen of the axis, it crosses the capsule of the atlanto-axial joint, and joins the retrograde branch of the occipital artery under cover of the great oblique muscle of the head. At each intervertebral foramen a =spinal branch= (Ramus spinalis) is given off which enters the vertebral canal and reinforces the ventral spinal artery. It also gives off series of dorsal and ventral =muscular branches= (Rami musculares). The dorsal branches are the larger; they supply the deep extensor muscles of the head and neck, and anastomose with the deep cervical and occipital arteries. The ventral branches supply chiefly the scalenus, longus colli, intertransversales, and rectus capitis anterior major. The artery is accompanied by the vertebral vein and a sympathetic nerve-trunk.

In some cases the last cervical transverse process has a foramen transversarium, through which the artery passes.

4. The =internal thoracic artery= (A. thoracica s. mammaria interna) is a large vessel which arises from the ventral side of the brachial opposite the first rib. It curves downward and backward, being at first on the inner surface of the rib, and then crosses the lower part of the first intercostal space and passes under the transversus thoracis muscle. It runs backward under cover of that muscle over the chondro-sternal joints to the eighth costal cartilage, where it divides into asternal and anterior abdominal branches. At each intercostal space two collateral branches are detached. The =intercostal branches= (Rami intercostales) pass upward in the intercostal spaces and anastomose with homonymous descending arteries. The lower branches detach small twigs to the transversus thoracis, pleura, and pericardium, and pass out between the costal cartilages as =perforating branches= (Rami perforantes) to supply the pectoral muscles and skin, anastomosing with the external thoracic artery. A very small pericardiaco-phrenic artery ascends in the mediastinum on the left side, in the caval fold of pleura on the right side; it supplies fine twigs to the pericardium and pleura and accompanies the phrenic nerve to the diaphragm. In the young subject it gives small branches (Aa. thymicæ) to the thymus gland. The =asternal artery= (A. musculophrenica) passes along the ninth costal cartilage and continues along the costal attachment of the transversus abdominis (Fig. 185). It gives off intercostal branches which anastomose with those descending from the thoracic aorta, and twigs to the diaphragm and transversus abdominis. The =anterior abdominal artery= (A. epigastrica cranialis) is the direct continuation of the internal thoracic. It passes between the ninth costal cartilage and the xiphoid cartilage, runs backward on the abdominal surface of the rectus abdominis and then becomes embedded in it (Fig. 466). It supplies the ventral wall of the abdomen and anastomoses with the posterior abdominal artery.

5. The =external thoracic artery= (A. thoracica externa) is given off from the ventral aspect of the brachial, usually at the inner surface or anterior border of the first rib. It turns around the first rib below or behind the brachial vein (when given off within the thorax) and passes backward under the deep pectoral muscle; it is continued as a small vessel in the panniculus carnosus, where it accompanies the external thoracic (“spur”) vein. It sends branches to the pectoral muscles and the axillary lymph glands.

This artery varies in origin and size. Not rarely it arises from the internal thoracic or from the brachial outside of the thorax. In other cases it arises by a common trunk with the inferior cervical. It may be very small or even absent, in which case the perforating branches of the internal thoracic compensate.

6. The =inferior cervical artery= (Truncus omo-cervicalis) arises usually from the dorsal surface of the brachial opposite the first rib or where that vessel winds around the rib. It is directed downward and a little forward across the external surface of the jugular vein and the deep face of the scalenus among the lymph glands at the thoracic inlet, and divides into ascending and descending branches. The =ascending branch= (A. cervicalis ascendens) passes upward and forward along the external surface of the jugular vein, then turns sharply backward and runs upward along the anterior border of the anterior deep pectoral muscle, between the omo-hyoideus and mastoido-humeralis and in relation to the prescapular lymph glands; it gives branches to these muscles and the prepectoral and prescapular lymph glands. The =descending branch= (A. transversa scapulæ) passes downward and outward across the surface of the anterior deep pectoral and then runs in the groove between that muscle and the mastoido-humeralis in company with the cephalic vein. It supplies branches to these muscles and the skin of the breast.

THE COMMON CAROTID ARTERY

These two vessels (Arteriæ carotides communes) arise from the brachiocephalic artery by a common trunk. This stem, the =truncus bicaroticus= or =cephalic artery=, is detached from the inner face of the brachiocephalic opposite the first rib and passes forward in the median plane beneath the trachea. It is related ventrally to the prepectoral lymph glands, the terminal parts of the jugular veins, and the anterior vena cava, and laterally to the vagus and recurrent nerves. It is commonly two or three inches (ca. 5 to 7 cm.) in length, but it may vary between one and eight inches (ca. 2.5 to 20 cm.).

FIG. 431.—VESSELS AND NERVES OF NECK OF HORSE.

a, Mastoido-humeralis; b, sterno-cephalicus; c, omo-hyoideus; d, sterno-thyro-hyoideus; e, trachea; f, position of cariniform cartilage; g, anterior superficial pectoral muscle; h, scalenus; i, intertransversales; k, insertion of serratus cervicis; l, origin of trapezius; m, rhomboideus; n, splenius; o, complexus; p, q, trachelo-mastoideus; p′, q′, tendons of same; r, longissimus; s, obliquus capitis posterior; t, wing of atlas; u, parotid gland; v, supraspinatus; w, anterior deep pectoral; x, spine of scapula; y, prescapular lymph glands; 1, external maxillary vein; 2, 3, jugular vein; 4, carotid artery, exposed by drawing jugular vein aside; 5, 6, ascending and descending branches of inferior cervical artery; 7, cephalic vein; 8, branches of superior or deep cervical artery; 9–14, ventral branches of second to seventh cervical nerves; 15, branches of dorsal divisions of cervical nerves. (Ellenberger-Baum, Top. Anat. d. Pferdes.) ]

The =right common carotid artery= passes obliquely from the ventral face of the trachea to its right side. In this position it runs upward and forward and divides at the crico-pharyngeus muscle and under the submaxillary gland into external carotid, internal carotid, and occipital arteries. It is inclosed in a fibrous sheath, and is accompanied dorsally by the vagus and sympathetic nerves, ventrally by the recurrent nerve. At the last two cervical vertebræ it is in contact superficially with the jugular vein, but further forward the omo-hyoideus muscle intervenes between the artery and vein. Near its termination the artery becomes more deeply placed and is related externally to the submaxillary and parotid glands, internally to the œsophagus. In some cases it is in contact ventrally with the thyroid gland, especially when the latter is larger than usual.

The =left common carotid artery= differs from the right one in that it is related deeply to the œsophagus, which separates it from the trachea in the greater part of its course.

The collateral branches of the common carotids are in the main small. They comprise:

1. =Muscular branches= (Rami musculares) of variable size, which go to the ventral muscles of the neck and the skin.

2. =Œsophageal= and =tracheal branches= (Rami œsophagei et tracheales). Small twigs go to the cervical lymph glands also.

3. The =parotid artery=. This comes off near the termination and enters the ventral part of the parotid gland. It also supplies the subparotid lymph glands, and sometimes sends a branch to the submaxillary gland. It is inconstant.

4. The =thyro-laryngeal artery= (A. thyreoidea cranialis). This, the largest collateral branch of the carotid, arises from the latter two or three inches before it divides. It curves over the anterior end of the thyroid gland, into which it sends several branches. It gives off a =laryngeal branch= (A. laryngea), which sends twigs to the external muscles of the larynx and the constrictors of the pharynx, passes between the cricoid and thyroid cartilages, and supplies the internal muscles and the mucous membrane of the larynx. A small =pharyngeal branch= (A. pharyngea ascendens) runs upward and forward to the crico-pharyngeus, and supplies twigs to the posterior part of the pharynx and the origin of the œsophagus. Small innominate twigs are given off to the trachea, the œsophagus, and the sterno-thyro-hyoideus and omo-hyoideus muscles.

In some cases the thyroid and laryngeal arteries arise from the carotid separately or by a short common stem. A laryngeal branch is often detached from the carotid in front of the thyro-laryngeal and enters the larynx with the superior laryngeal nerve. The pharyngeal branch frequently comes directly from the carotid.

FIG. 432.—CROSS-SECTION OF NECK OF HORSE, PASSING THROUGH FIFTH CERVICAL VERTEBRA; ANTERIOR VIEW.

a, Branches of cervical nerves; a′, nuchal fat; b, intertransversalis muscle; c, longissimus muscle; d, vertebral artery; e, vertebral vein; f, vertebral nerve; g, spinal accessory nerve (upper division); h, recurrent nerve; i, vago-sympathetic trunk; k, tracheal lymph duct; l, body of fifth cervical vertebra; l′, transverse process of same; m, carotid artery; n, jugular vein; o, superior cervical artery; o′, satellite vein of o; p, spinal cord; q, dura mater; r, spinal vein; s, ligamentum nuchæ; t, rhomboideus muscle; u, splenius; v, complexus; w, multifidus; x, serratus cervicis; y, mastoido-humeralis; z, sterno-cephalicus; 1, rectus capitis ant. major; 2, omo-hyoideus; 3, panniculus; 4, sterno-thyro-hyoideus; 5, longus colli; 6, 7, trachelo-mastoideus; 8, trapezius; 9, spinalis; 10, œsophagus; 11, trachea, with cartilaginous ring (11′), mucous membrane (11″), and muscular layer (11‴). (After Ellenberger, in Leisering’s Atlas.) ]

5. The =accessory thyroid artery= (A. thyreoidea caudalis) is an inconstant vessel which arises from the carotid at a variable distance behind the thyro-laryngeal—sometimes from the latter or from the parotid artery. It sends branches into the posterior part of the thyroid gland and detaches small tracheal and muscular twigs. In some cases it is distributed chiefly or entirely to the adjacent muscles.

THE OCCIPITAL ARTERY

FIG. 433.—DEEP DISSECTION OF NECK OF HORSE.

a, a, Ends of sterno-cephalicus; b, anterior part of omo-hyoideus; c, sterno-thyro-hyoideus; d, trachea; e, œsophagus; f, cariniform cartilage; g, rectus cap. ant. major; h, stump of trachelo-mastoideus; i, intertransversales; k, multifidus; l, m, scalenus; n, serratus cervicis; o, o, stumps of splenius, p, longissimus, q, complexus (most of which is removed); r, rhomboideus; s, trapezius; t, spinalis et semispinalis; u, lamellar part of lig. nuchæ; v, mastoido-humeralis; w, anterior deep pectoral; x, supraspinatus; y, anterior superficial pectoral; z, scapular tuberosity; 1, 1, articular processes of cervical vertebræ; 2, 2, transverse processes of same; 3, atlas; 3′, axis; 4, 4, jugular vein (remainder removed); 5, common carotid artery, from which a piece is removed to show the accompanying nerves; 6, vago-sympathetic trunk; 7, 7, tracheal and muscular branches of carotid artery; 8, recurrent nerve; 10, left tracheal lymph duct; 11, 12, ascending and descending branches of inferior cervical artery (13); 14, cephalic vein; 15–20, ventral branches of second to seventh cervical nerves; 21, roots of phrenic nerve; 22, thoracic or pectoral nerves; 22′, nerve to serratus magnus; 23, musculo-cutaneous nerve; 24, median nerve; 25, ulnar nerve; 26, radial nerve; 27, axillary nerve; 28, dorsal branches of cervical nerves; 28′, accessory nerve (cut); 29, superior or deep cervical artery; 30, muscular branch of vertebral artery; 31, posterior (anastomotic) branch of occipital artery; 32, vertebral artery; 33, muscular branches of occipital artery; 34, obliquus capitis post.; 35, obi. cap. ant.; 36, twig from dorsal branch of third cervical nerve. (After Ellenberger-Baum, Top. Anat. des Pferdes.) ]

The =occipital artery= (A. occipitalis) is the second in size of the terminals of the carotid. It arises usually just in front of the internal carotid, but in some cases with that artery by a common trunk of variable length. It pursues a somewhat flexuous course to the fossa atlantis, where it divides into anterior and posterior branches. It is related superficially to the submaxillary gland and the mastoido-humeralis, and deeply to the guttural pouch and the rectus capitis anterior major. The internal carotid artery, the inferior cerebral vein, and the accessory, vagus, and sympathetic nerves cross its deep face. It gives twigs to the submaxillary gland, the anterior straight muscles, the guttural pouch and the adjacent lymph glands, and two named collateral branches. The =condyloid= or =prevertebral artery= (A. condyloidea) is a small vessel which passes upward and forward on the guttural pouch, and divides into muscular and meningeal branches. The latter enter the cranium through the foramen lacerum and hypoglossal foramen and are distributed to the dura mater. This artery is very variable in its origin. The =posterior meningeal= or =mastoid artery= (A. meningea caudalis) is a much larger vessel which runs upward and forward between the small oblique muscle and the paramastoid process, passes through the mastoid foramen into the parieto-temporal canal, enters the cranial cavity, and is distributed to the dura mater.

FIG. 434.—VESSELS AND NERVES OF BASE OF BRAIN OF HORSE.

13, Cerebro-spinal artery; 14, middle spinal artery; 15, basilar artery; 16, posterior cerebellar artery; 17, anterior cerebellar artery; 18, internal auditory artery; 19, posterior cerebral artery; 20, deep cerebral artery; 21, stump of internal carotid artery; 22, anterior choroid artery; 23, anterior meningeal artery; 24, middle cerebral artery; 25, artery of corpus callosum; 26, anterior communicating artery; 1, 1′, 1″, olfactory tracts; 1‴, olfactory peduncle; 2–12, cranial nerves; a, olfactory bulb; b, trigonum olfactorium; c, lamina perforata anterior; d, fossa transversa; e, pyriform lobe; f, cerebral peduncle; g, tractus transversus; h, corpus mammillare; i, tuber cinereum; k, lateral fissure (of Sylvius); l, presylvian fissure; m, pons; o, pyramid; p, facial eminence; q, corpus restiforme; r, cerebellum; s, middle peduncle of cerebellum. (After Ellenberger Baum, Top. Anat. d. Pferdes.) ]

The =posterior= or =retrograde branch= (Ramus descendens) of the occipital passes up through the foramen transversarium of the atlas and joins the vertebral artery. It gives branches to the great oblique muscle of the head, which covers it.