50 VERTEBRATE ZOOLOGY 



sel sends off four pairs of afferent branchial arteries which carry 

 blood to the gills ; four pairs of efferent branchial arteries then run 

 from the gill arches dorsally to the median plane, where they form 

 the aorta descendens, or dorsal aorta. 



Springing from the dorsal end of the first (anterior) efferent 

 branchial artery, on each side, is the large carotid artery, which 

 supplies the head ; it soon divides into two branches, which pass, 

 respectively, above and below the eye. The dorsal aorta passes 

 along the dorsal side of the body cavity, just beneath the spinal 

 column, to the posterior end of the body; in the caudal region 

 it becomes the caudal artery and lies in the ventral arches of 

 the vertebrae. It gives off the paired spinal arteries along its en- 

 tire course : the cceliac artery, a large median vessel which leaves 

 the aorta a short distance back of the branchial arteries and, 

 breaking up into a number of branches, supplies the digestive 

 tract, air bladder, and genital glands; and the two subclavian 

 arteries, which leave the aorta just back of the coeliac artery and 

 go to the pectoral fins. 



First study the ventral aorta and the afferent branchial arteries. 

 Entirely remove the lower jaw and the left opercle, but do not 

 disturb the gill arches; with scissors cut off the gills from the 

 arches. Follow the ventral aorta from the bulbus arteriosus for- 

 ward between the ventral ends of the gill arches. Find the points 

 where the four afferent arteries on the left side leave the aorta, 

 and trace the course of each along the hinder side of the gill arches ; 

 the transparency of the skin covering the gill arches permits this 

 to be done easily. 



The remaining arteries will be studied after the veins. 



Exercise 20. Draw the arteries just observed. 



The Veins (Continued)} The following are the systemic veins, 

 which carry blood directly to the heart. The short hepatic vein 

 enters the sinus venosus in the median plane. Press the liver away 



1 The veins are easily studied without injection, as the death of the animal 

 leaves them filled with blood. If it is wished to inject them, however, this may 

 be done through the caudal vein, which is the lowermost of the two vessels in the 

 ventral canal of the vertebral column. 



