190 VERTEBRATES. 



Three terms which apply to muscles need to be learned : 

 (1) the thick, swollen central part is called the belly of 

 the muscle; (2) that end of the muscle which is most 

 fixed in position, and toward Avhich, when it contracts, 

 the muscle pulls, is called its origin; (3) the attachment 

 of its other, freer end is called its insertion. 



Relations of Muscles, Blood Vessels, and Nerves. 

 Dissect away the large muscles of the thigh and shank 

 by cutting transversely through the belly of each, and dis- 

 secting each way, so as to find the origin and insertion of 

 each, and having care not to cut blood vessels or nerves. 

 Trace the great sciatic nerve of the thigh. Follow its two 

 principal branches down into the foot. Find and dis- 

 tinguish two large, branching blood vessels in the thigh, 

 the femoral artery and vein. This dissection, if thought- 

 fully performed, will enable you to answer the following 

 questions : 



1. Where, with reference to the joints, are the thickest 

 portions of the leg ? 



2. What give these points their thickness ? 



3. What advantage is there in the tendonous termina- 

 tions of the muscles at the joints ? 



4. Where are the bones thickest ? 



5. What are the ridges on the bones for ? 



6. Which lie deeper in the muscles, arteries of veins ? 



7. Why are the principal nerves so remote from the 

 surface ? 



8. Why are the insertions of these muscles all at their 

 outer ends ? 



Separate the thigh and the shank at the knee joint, and 

 observe the firm, white, elastic cartilage forming the 

 articulating surface. 



Dermis and Epidermis. After the skin has been lying 

 in water for half a day, observe that there is an outer 



