260 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



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

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

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

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

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

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

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

 Draw the branches of the common carotid artery. 



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

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

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

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

 between the aorta and the pulmonary (Fig. 58, p. 267). "Follow the aorta pc 

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

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

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

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

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

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

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

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

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

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

 with the jugular vein, generally at the point of union with the subclavian, m< 

 be found. 



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

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

 the abdominal aorta. 



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

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

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

 surface of the aorta. Follow it identifying its branches. These branches co 

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

 ■visceral branches to the kidneys and reproductive organs, and paired somai 

 branches to the body wall. 



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

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

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

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

 vessels are different in the two animals owing to the differences in their dige 

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



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

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



