A TURTLE 157 



with the right aorta. It gives off the following large arteries : the 

 cceliac artery, which passes to the wall of the stomach, where it 

 breaks into branches ; the anterior mesenteric artery which supplies 

 almost the entire intestine, its numerous branches lying alongside 

 those of the mesenteric vein; the gastroduodenal artery, which 

 divides into two main branches and supplies the stomach, duode- 

 num, and pancreas. Trace all these arteries and their branches. 



In young animals and sometimes in adults a small cross artery 

 will be seen on each side, which unites the aorta with the pulmo- 

 nary artery ; it is called the ductus Botalli. 



Follow the dorsal aorta now to the hinder end of the body cavity, 

 where it passes between the kidneys alongside the postcaval vein, 

 and behind them divides into the right and left common iliac 

 arteries. A number of small arteries will be seen leaving the dorsal 

 aorta, one of which, the epigastric artery, passes to the lateral 

 border of the carapace, on each side, where it runs forward and 

 finally anastomoses with the internal mammary artery. Trace 

 these small arteries. 



Each common iliac artery divides very soon into the internal and 

 the external iliac. The former gives off branches which supply 

 the colon, rectum, and cloaca. The latter gives off branches to the 

 muscles of the pelvis, and then, as the sciatic artery, supplies the 

 leg. Follow the sciatic and its branches. 



Exercise 33. Draw a diagram of the arterial system so far as observed. 

 Exercise 34. Draw a diagram of the entire vascular system. 



The Brain and the Cranial Nerves. Cut off the head. With a 

 strong scalpel or bone-forceps cut the bone from the dorsal side 

 of the cranium and also partly from the lateral sides ; carefully re- 

 move the dura mater — the connective-tissue membrane covering 

 the brain— and study its dorsal , surface. Its anterior division, 

 the cerebrum, makes up more than half the brain ; it is composed 

 of the two hemispheres, from the forward end of which project 

 the olfactory lobes. Between the posterior ends of the hemi- 

 spheres is the dark-colored anterior choroid plexus, which forms 

 the dorsal wall of the diencephalon, the second division of the 

 brain. Back of this appear the paired optic lobes, the dorsal por- 



