The Blood-Vascular System of the Ox

The Pericardium and Heart

The pericardium is attached by two fibrous bands (Ligamenta sternopericardiaca) to the sternum opposite the facets for the sixth costal cartilages; these ligaments, right and left, are embedded in the mass of fat which separates the apex of the pericardium from the floor of the thorax.

The heart of the adult ox has an average weight of about 5½ to 6 pounds (ca. 2.5 to 2.7 kg.), or about 0.4 to 0.5 per cent. of the body-weight. Its length from base to apex is relatively longer than that of the horse and the base is smaller in both its diameters.

A shallow intermediate groove (Sulcus intermedius) extends from the coronary groove down the left side of the posterior border, but does not reach the apex. The amount of fat in and near the grooves is much greater than in the horse.

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. ). 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.