THE PERCH 211 



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

 form the dorsal aorta. 



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

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

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

 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 Hes in the ventral arches of the vertebrae. 

 It gives off the paired spinal arteries along its entire 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 cceliac artery and go 

 to the pectoral fins. 



First study the ventral aorta and the afferent branchial ar- 

 teries. Entirely remove the lower jaw and the left operculum, 

 but do not disturb the gill arches ; with scissors cut off the gills 

 from the arches. Follow the ventral aorta from the bulbus 

 arteriosus forward 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 14. Draw the arteries just observed. 



The Venous System (Continued)} The following are the sys- 

 temic veins, which carry blood directly to the heart. The short 

 hepatic vein enters the sinus venosus in the median plane. Press 

 the liver away from the false diaphragm and find it. Joining each 

 end of the transverse sinus venosus is a large and conspicuous 



^ 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.. 



