VAN 211: Veterinary Histology and Embryology (2+2)

ARTERIES

• The aorta is dilated at its origin forming the aortic sac from which the ventral aortae ascend and continue as right and left dorsal aortae. The dorsal aortae unite behind to form a single descending aorta.
• From the aortic sac, five pairs of aortic arches arise and connect themselves to the dorsal aortae. The pulmonary artery divides into right and left pulmonary arteries which connect themselves by the sixth aortic arches with the dorsal aortae.
• The first and second aortic arches of both sides degenerate. The dorsal aortae between the third and fourth arches degenerate, thus establishing continuity between the third arches and the anterior segments of the dorsal aortae. The third aortic arch gives off a sprout - the external corotid artery, after which it is continued as the internal carotid artery.
• The common stem of the third arch before the sprout arises is the common carotid artery. The fourth arches are transformed into different structures on both sides. The right arch becomes the right subclavian artery (right axillary).
• The fourth arch on the left side persists as the arch of the aorta and gives off a sprout,the left subclavian artery (left axillary). The fifth arches degenerate. The sixth arches (pulmonary arches) on the right side degenerates, whereas on the left side it persists as the ductus arterious.
• The vagi detach the recurrent laryngeal nerves which pass round the sixth arches. During the migration of the heart downwards, the left recurrent laryngeal nerve, hooks around the sixth arch (ductus arteriosus) and is dragged down whereas the right nerve lags behind and is hooked around right brachial. The right dorsal aorta between the sixth arch and the descending aorta degenerates.

• In the domestic animals the right brachial and the right common carotid shift themselves on the arch of the aorta and fuse with the left common carotid and the left brachial.
• The dorsal aorta gives off the following branches:
  • The ventral splanchnic arteries which are represented in the adult by the coeliac anterior and posterior mesenteric arteries.
  • The lateral splanchnic arteries represented in the adult by the renal, adrenal, testicular and ovarian arteries.
  • The dorsal inter segmental arteries with divide into dorsal and ventral ramus. The dorsal ramus gives a spinal branch to form the inferior spinal artery and passes up to supply the muscles and skin of the back. The ventral ramus supplies the body wall and is represented in the adult by the intercostal arteries in the thoracic and lumbar arteries in the lumbar regions.
• The dorsal aorta terminates by giving off two umbilical arteries after which it is continued by the middle sacral artery. The external iliac arteries are sprouts from the umbilical arteries. A new connecting trunk from the junction of the umbilical artery with aorta, becomes the internal iliac.