NECTURUS 13 



and trace the aorta and postcardinal veins forward, stripping off 

 the skin to see the parts more clearly. At the level of the 

 shoulder-girdle the aorta gives off a subclavian artery on either 

 side, in front of which it divides into two vessels, the radices 

 aortse. Lateral to the radices are the anterior ends of the post- 

 cardinal veins. Trace them as they bend to enter the sinus 

 venosus. This portion is called the ductus Cuvierii. 



Follow one radix aortaB forward into the gill region, noting the 

 vertebral artery which it gives off on its medial side. In front 

 of the origin of the vertebral the radix bends laterally to pass, 

 as the second efferent branchial artery, along the dorsal side of 

 the middle gill, receiving in its course a third efferent artery from 

 the last gill. At the point of bending the radix is connected by 

 a smaller vessel with a similar first efferent branchial artery 

 which comes from the first gill. From this first efferent artery an 

 external carotid artery is given off which passes downward and 

 forward, while the common trunk of radix and first efferent 

 continues toward the middle line as the internal carotid artery. 



Also note, proceeding backwards from the third efferent 

 branchial , the pulmonary artery, which should be traced to the 

 lung of the same side. 



Add these vessels to your drawing. 



The venous trunks of the head are more difficult to follow. 

 Follow the anterior cardinal or jugular vein forward from the 

 ductus Cuvierii, noting its branches: first a subclavian vein, 

 next a division into internal jugular, coming from the brain, and 

 external jugular vein, from the face and lower jaw. See also 

 a lateral vein entering the Cuvierian duct of either side and trace 

 it back into the side walls of the body. 



Add these vessels to the sketch and then follow out and add 

 the remainder of the pulmonary artery and the subclavian artery 

 and vein. Note, arising from the subclavian artery and passing 

 back near the mid-ventral line of the ccelom, a cutaneous artery. 



(The head may now be cut from the trunk and placed for a 

 day or two in nitric alcohol to decalcify it for the study of the 

 brain. While this is being done the skeleton (p. 15) may be 

 studied.) 



The Brain. Take the head from the nitric alcohol, rinse for 

 15 minutes in running water, and then very carefully remove 

 muscles and decalcified bone from the roof until the whole top 



