24 VERTEBRATE ZOOLOGY 



Find and trace the branch of the first efferent artery which goes 

 forward and supplies the head. This is the common carotid artery ; 

 in the smooth dogfish it is joined by a branch of the dorsal aorta. 



The efferent arteries meet in the median plane and form the 

 dorsal aorta. Issuing from the aorta between the third and fourth 

 efferent arteries is a pair of small subclavian arteries, one of which 

 extends to the pectoral fin on each side. 



Exercise 25. Draw a diagrammatic sketch of the efferent branchial 

 arteries and their branches. 



The dorsal aorta is a large median artery which lies just beneath 

 the spinal column in the body cavity ; back of the anus it becomes 

 the caudal artery, which lies in the ventral arches of the vertebral 

 column. It gives off several arteries, some of which are paired ves- 

 sels and others of which are median. The median arteries are the 

 following : the cceliac artery, a large vessel which arises from the 

 aorta near its anterior end and passes backward to the V-shaped 

 portion of the stomach, where it sends branches to the stomach, 

 liver, intestines, pancreas, gonads, and spleen ; the anterior mesen- 

 teric and gastrosplenic arteries, which leave the aorta near to- 

 gether at about the middle of its course and send branches to the 

 stomach, spleen, pancreas, and intestine ; the posterior mesenteric 

 artery, which arises from the aorta near its hinder end and passes 

 to the rectal gland. The paired arteries are the following: the 

 parietal arteries, small vessels arising from the aorta at regular 

 intervals and passing to the muscles of the body wall ; the genital 

 arteries, which supply the reproductive organs ; the renal arteries, 

 small paired arteries which leave the aorta at intervals along its 

 course and go to the dorsal surface of the kidneys ; the iliac arte- 

 ries, a pair of small paired arteries which go to the ventral fins. 



Exercise 26. Draw a diagrammatic sketch of the dorsal aorta and its 



branches, so far as observed. 

 Exercise 27. Draw a diagram of the entire vascular system. 



The Body Muscles. Remove the skin from a part of the body 

 in the caudal region and study the muscles which form the sides 

 of the body. On each side a series of muscle segments is present 



