260 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



At the angle of the jaw it branches to all parts of the head. Its chief branches 

 are : the lingual artery into the tongue and the external maxillary running along 

 the ventral border of the masseter muscle and branching to the upper and lower 

 lips and jaws. The main artery then passes along the posterior border of the 

 masseter muscle. It receives auricular and temporal branches from the pinna 

 and temporal regions and then, as the internal maxillary artery, turns internal 

 to the masseter muscle and is lost to view. It need not be followed farther. 

 Draw the branches of the common carotid artery. 



c] The thoracic aorta: After having given rise to the subclavians and the 

 carotids, the aorta arches to the left. Note as it passes the left pulmonary, the 

 strong fibrous band which connects the two vessels. This is the arterial liga- 

 ment or ligament of Botallus and is the remnant of the embryonic connection 

 between the aorta and the pulmonary (Fig. 58, p. 267). Follow the aorta pos- 

 teriorly, pressing the left lung to the right. It descends posteriorly lying against 

 the dorsal wall of the thorax to the left of the median line. It is situated within 

 the mediastinum; the mediastinal wall may be cleared away. The aorta in its 

 course along the thorax is named the thoracic aorta. Its chief branches are the 

 paired intercostal arteries which arise from the aorta at segmental intervals and 

 run along the thoracic wall along the posterior margin of the ribs. The aorta 

 also has small bronchial arteries to the bronchi and esophageal arteries to the 

 esophagus. Along the dorsal surface of the aorta on its left side runs a delicate 

 tube, resembling a streak of fat. This is the thoracic duct, the main lymphatic 

 channel for the posterior part of the body. Trace it forward; its connection 

 with the jugular vein, generally at the point of union with the subclavian, may 

 be found. 



The aorta penetrates the diaphragm to which in the rabbit it gives superior 

 phrenic arteries and passes into the peritoneal cavity where it is known as 

 the abdominal aorta. 



d) The abdominal aorta: Turn the digestive tract to the right and locate 

 the dorsal aorta after it has passed the diaphragm. It will be found against the 

 dorsal wall in the median dorsal line. Clear away the mesogaster and clean the 

 surface of the aorta. Follow it identifying its branches. These branches con- 

 sist of unpaired median visceral branches to the digestive tract, paired lateral 

 visceral branches to the kidneys and reproductive organs, and paired somatic 

 branches to the body wall. 



Shortly posterior to the diaphragm the aorta gives rise to two large unpaired 

 visceral arteries, the coeliac and the superior mesenteric arteries. In the cat the 

 second is shortly posterior to the first, while in the rabbit the superior mesenteric 

 artery lies one-half inch posterior to the coeliac. As the branches of these two 

 vessels are different in the two animals owing to the differences in their diges- 

 tive tracts, it will be necessary to describe them separately. 



Rabbit: The coeliac artery near its origin from the aorta gives rise to the 

 small inferior phrenic arteries to the diaphragm. Beyond this point the splenic 



