DISSECTING. 119 



lies on the floor of the body cavity and in a portion of its 

 course is covered by bony arches. These must be broken 

 down. The homologies of the legs and mouth parts should 

 also be investigated. The gills will be found under the sides 

 of the carapax. The relations and motions of the teeth found 

 in the stomach will prove an interesting subject for study. 

 Insects are dissected in much the same way as lobsters, but 

 from their smaller size require more delicate manipulation. 



Frogs are one of the best of vertebrates for study. In inves- 

 tigating the visceral anatomy they should be killed by pithing; 

 a needle is forced into the spinal canal at the base of the skull 

 and forced down the canal and also into the brain. The frog 

 is now opened in the median ventral line and the parts care- 

 fully dissected out. The heart will continue beating for a 

 considerable time after the animal has been killed. The 

 brain is studied by opening the skull from the top. The 

 muscles are easily dissected, their origin and insertion readily 

 seen and the results produced by each one, readily under- 

 stood. Fishes and many mammals are generally opened from 

 the side. The left side is the one usually chosen, the head 

 being directed toward the left hand of the operator. 



The amount of time which can be advantageously spent 

 on a single form or even on a single specimen is very great. 

 In studying the anatomy of any form there should be no 

 haste. Not a single cut should be made until the student 

 realizes just why and what results will follow. It is far better 

 to know the structure of one form well than to have a super- 

 ficial and very vague idea of a dozen or more forms. 



