34 GENERAL BIOLOGY 



(g) The sciatic artery is the continuation of the iliac artery 

 in the leg. Soon after entering the leg the sciatic 

 gives off a large branch, the femoral artery, which 

 supplies blood to the thigh muscles. At the knee 

 the sciatic divides into two chief branches, the tibial 

 extending along the front of the leg into the foot, and 

 the peroneal which passes along the back of the leg 

 into the calf muscles. 



Make a large drawing of the heart and arterial 

 system, carefully showing the origin and distribution 

 of the vessels studied. 



3. Veins. While the arteries have been under investi- 

 gation it will have been noticed that there were other vessels, 

 not injected, running parallel with the arteries. These were 

 some of the larger veins of the body. The veins make up a 

 system for the return of the blood to the heart, but their 

 further study will not be attempted here. 



Before leaving the study of the circulatory system one 

 should see the circulation of blood in a living frog. This 

 may easily be done by examining with a microscope the 

 thin web in the foot of an anesthetized animal. 



V. Nervous System. 



The nervous system consists of three general divisions; 

 the central, composed of the brain and spinal cord; the 

 peripheral, which includes the nerves connecting the central 

 system with sense organs and muscles; the sympathetic, a 

 series of nerves extending to the internal organs. 



1. The Central System. Place the frog dorsal side upper- 

 most and slit the skin along the median line from the snout 

 to the anus. Lift up the cut edges and notice the pairs of 

 delicate thread-like nerves which run through the muscles 



