Part 185

The heart is situated more to the left of the median plane than in the horse and is opposite to the third, fourth, and fifth ribs when it is contracted. It has extensive contact with the lateral wall of the thorax on the left side, but none on the right side, where a considerable thickness of lung covers the pericardium.

Two bones, the =ossa cordis=, develop in the aortic fibrous ring. The right one is in apposition with the atrio-ventricular rings and is irregularly triangular in form. Its left face is concave and gives attachment to the right posterior cusp of the aortic valve. The right surface is convex from before backward. The base is superior. The posterior border bears two projections separated by a notch. It is usually a little more than an inch (ca. 4 cm.) in length. The left bone is smaller and is inconstant. Its concave right border gives attachment to the left posterior cusp of the aortic valve. There is a large fleshy moderator band in the right ventricle.

THE ARTERIES

The great arterial trunks in the thorax resemble those of the horse in general disposition.

The =left coronary artery= is much larger than the right one; it gives off a branch which descends in the intermediate groove, and terminates by running downward in the right longitudinal groove. The =right artery=, after emerging from the interval between the right auricle and the pulmonary artery, divides into branches which are distributed to the wall of the right ventricle.

The =brachiocephalic trunk= (anterior aorta) is usually four or five inches (ca. 10 to 12 cm.) in length.

The =brachial arteries= give off in the thorax the following branches:

1. A common trunk for the subcostal, dorsal, superior or deep cervical, and vertebral arteries.

(1) The =subcostal artery= commonly arises separately, but may be given off as in the horse. It supplies the first three intercostal arteries.

(2) The =dorsal artery= is relatively small. It usually ascends in front of the first costo-vertebral joint and is distributed as in the horse.

(3) The =superior= or =deep cervical artery= may arise from a common stem (Truncus vertebro-cervicalis) with the vertebral, or may constitute a branch of that artery. It passes up between the first thoracic and last cervical vertebræ or between the sixth and seventh cervical and is distributed as in the horse.

(4) The =vertebral artery= passes along the neck as in the horse to the intervertebral foramen between the second and third cervical vertebræ, gives off a muscular branch, and enters the vertebral canal (Fig. 469). It runs forward on the floor of the canal—connected with its fellow by two or three transverse anastomoses—and divides in the atlas into two branches. The smaller internal division (cerebrospinal artery) passes forward to the floor of the cranium and concurs with the condyloid artery and branches of the internal maxillary in the formation of a large =rete mirabile=. The large external branch emerges through the intervertebral foramen of the atlas and ramifies in the muscles of the neck in that region, compensating for the smallness of the branches of the occipital artery. It also sends a branch to the rete mirabile. The collateral branches detached to the cervical muscles are large and compensate for the small size of the deep cervical artery. The collateral spinal branches of the vertebrals pass through the intervertebral foramina, divide into anterior and posterior branches, and form two longitudinal trunks which are connected by cross-branches so as to form irregular polygonal figures.

2. The =internal thoracic artery=.

3. The =inferior cervical artery= corresponds usually to the ascending branch of that vessel in the horse.

4. The =external thoracic artery= is large and usually gives off a branch which is equivalent to the descending branch of the inferior cervical artery of the horse.

THE COMMON CAROTID ARTERY

FIG. 468.—SCHEMA OF CHIEF ARTERIES OF HEAD OF COW.

1, Common carotid artery; 2, thyro-laryngeal; 3, thyroid; 4, laryngeal; 5, pharyngeal; 6, occipital; 7, condyloid; 8, middle meningeal; 9, pharyngeal; 10, external maxillary; 11, lingual; 12, sublingual; 13, superior labial; 14, internal maxillary; 15, masseteric; 16, inferior alveolar; 17, buccinator; 18, great palatine; 19, sphenopalatine; 20, posterior auricular; 21, superficial temporal; 22, posterior meningeal; 23, anterior auricular; 24, artery to matrix of horn; 25, deep temporal; 26, arteries to rete mirabile; 27, frontal; 28, malar; 28′, dorsal nasal continuation of malar; 29, infraorbital; 29′, lateral nasal continuation of 29. ]

The =carotid arteries= usually arise from a common trunk about two inches (ca. 5 cm.) in length, but in exceptional cases are given off separately from the brachiocephalic. Each pursues a course similar to that of the horse and is accompanied by the small internal jugular vein, but is separated from the external jugular vein by the omo-hyoid and sterno-mastoid muscles. It divides at the digastricus into occipital, external maxillary, and external carotid arteries. In addition to tracheal, œsophageal, and muscular branches, it gives off the thyroid and laryngeal arteries. The =thyroid artery= (A. thyreoidea cranialis) bends around the anterior end of the thyroid gland, in which it ramifies. The accessory thyroid artery is usually absent. The =laryngeal artery= may arise with the thyroid.

1. The =occipital artery= is relatively small. It gives off:

(1) The =pharyngeal artery=, which, however, may arise from the external carotid.

(2) Several branches to the muscles (chiefly the flexors) and to the atlanto-occipital joint.

(3) The =condyloid artery= passes into the cranium through the anterior foramen in the condyloid fossa, and joins the vertebral in the formation of the rete mirabile about the pituitary gland. Before entering the cranium it gives off a branch to the pharyngeal lymph glands, and the middle meningeal artery; the latter passes through the foramen lacerum. Another branch enters the temporal canal and gives twigs to the temporalis muscle and the mucous membrane of the frontal sinus. A muscular branch emerges from the intervertebral foramen of the atlas. A diploic branch goes into the occipital condyle and squama, and emits twigs to the occipital muscles.

FIG. 469.—FLOOR OF CRANIUM AND ANTERIOR PART OF VERTEBRAL CANAL OF OX.

1, Vertebral artery; 2, muscular branches of 1; 3, branches of 1 to the rete mirabile, 4; 5, branches of internal maxillary artery to rete; 6, branch of internal maxillary artery entering cranium through foramen ovale; 7, condyloid artery; 8, emergent artery from rete, distributed like internal carotid artery of horse; 9, 9′, longitudinal vertebral sinuses; a, cribriform plate; b, optic foramina; c, for. lacerum orbitale + rotundum; d, foramen ovale; e, occipital condyle; f, g, h, first, second, and third cervical vertebræ. (After Leisering’s Atlas.) ]

2. The =external maxillary artery= is smaller than that of the horse, but pursues a similar course. The =lingual artery= is large, and often arises separately from the common carotid; it gives off a branch to the submaxillary gland, and the =sublingual artery=. After turning around the jaw the facial gives off the two =labial arteries=. The =superior labial= is large; it usually gives off a branch which runs forward almost parallel with the lateral nasal. The =angular artery= is absent or rudimentary, and the =lateral= and =dorsal nasal arteries= spring from branches of the internal maxillary.

3. The =external carotid artery= passes upward between the stylo-hyoideus and the great cornu of the hyoid bone, turns forward across the external face of the latter, and divides into superficial temporal and internal maxillary arteries. It gives off the following collateral branches:

(1) Branches to the parotid and submaxillary glands.