Branch Chordata ^^ 



Inside the mouth at the back find the eustachian tube, 

 a passage leading to the drum of the ear. 



INTERNAL ANATOMY 



III. — Dissection. With scissors or sharp scalpel cut the 

 skin from the edge of the lower jaw along the median 

 ventral line to the cloacal opening. Notice how loosely 

 the skin is attached to the body. Where is the prin- 

 cipal place of attachment.' Make lateral slits in the 

 skin and pull away the flaps, pinning them if necessary. 

 Remove the skin from the legs in the same manner. 

 Observe the development of the powerful chest muscles ; 

 also the muscles in the hind legs used as the propelling 

 power in long leaps. Next, cut the body wall from end 

 to end, in a similar manner to the incision of the skin, 

 being very careful not to disturb any of the viscera 

 beneath. Make lateral slits and pin back the flaps of 

 the body wall, exposing the internal organs. A circlet 

 of bones to which the legs are attached passes over the 

 chest just above the heart. Cut these with strong 

 scissors. 



IV. — General. Recalling the general plan on which the 

 earthworm and lobster are built, you will remember 

 that it is a tube within a tube. The wall of the outer 

 tube, being the body wall, encloses the body cavity ; 

 while the inner tube is the alimentary canal, with its 

 two openings. Find a similar structure now revealed 

 in the case of the frog. The large cavity holding the 

 various organs, or viscera, is the body cavity, or outer 

 tube, and through this passes the alimentary canal, or 

 inner tube. The latter is now partly visible as the 

 light-colored stomach or intestine. 



