HO THE FROG, OR THE TOAD. 



floor of the mouth? What advantage in this method of attach- 

 ment? 



1) In the back part of the mouth cavity, on the floor, is a short, centrally 

 located slit, the glottis. Through this slit air is forced into the 

 lungs from the mouth. Understand the several movements in 

 respiration that would contribute to this result. 



m) The anus is centrally located at the posterior end of the body. 



n) The male of some species of frogs has, at the corners of the mouth, 

 a loose fold of skin forming the vocal sac. This is inflated into a 

 globular form when the animal is calling. 



Exercise 2. Draw the hand and the foot of the frog, with the toes outspread. 



Technical Note. With a pair of scissors slit the skin along the mid-ventral 

 line from near the anus to the front angle of the lower jaw. Notice 

 how loosely it is attached to the muscular body wall beneath. Cut 

 transversely right and left from the extremities of the first incision, 

 lay the specimen on its back in a dissecting pan and pin out tlie 

 flaps of the skin. 



THE MUSCLES. The above partial dissection lays bare some of the 

 principal muscles of the body. If desired, the skin may be stripped 

 part way down the hind limbs, where the number and arrangement of 

 the muscles is very similar to that in human anatomy. Each muscle is 

 enclosed in a thin, transparent muscle sheath and is made up of many 

 bundles of fibers similarly enclosed. 



The muscles in the region of the arms are mainly attached to the 

 pectoral girdle, those connected with the legs to the pelvic girdle, of 

 which the pubic bone forms the center. The abdominal muscles are 

 broad and sheet-like. Mount a few muscle-fibers and study with the 

 microscope. 



Technical Note. Cut through the thin abdominal wall from the pubic bone 

 to the shoulder girdle. Separate tlie bones of the latter, cut trans- 

 versely right and left, as when removing the skin, and pin out the 

 flaps of muscle. Rinse with clear water as often as necessary. 

 Keep the specimen under water or weak alcohol if you prefer. 



