77//-; (>ir\L c.\ 1 /'/■]■ 19 



which in the t'roj^ represents the v(»ice box of hijfher animals. 

 These cartilages cannot he seen without dissection. .Inst beneath 

 the corners of the mouth are the openings of the vocal sdcs in the 

 male. 



Upon the plate showing the roof and floor of the mouth in 

 outline represent and label all the oral structures mentioned 

 above. 



THE VISCERA 



Lay the frog on its back under water. Hy passing pins through 

 the Hmbs fasten it to the wax bottoin of a tray. Cut through 

 the skin, along the middle line, the whole length of the ventral 

 surface. Separate the skin from tiie underlying parts The 

 muscles of the ventral body wall and the pectoral girdle should 

 now be exposed. Note a dark blue streak running along the 

 mesal longitudinal line just beneath the muscular walls. This 

 line represents the location of the ventral ahdominal vein. With 

 forceps pinch up the muscular body wall and with scissors cut 

 through it into the celom (body cavity) a little to the left of the 

 median line. Continue this cut caudad to the end of the body 

 and cephalad to the jaws, cutting through the pectoral girdle 

 with strong scissors, taking care not to injure the parts beneath. 

 If incisions taking a lateral course be made through the body wall 

 and skin in the region of the pelvic girdle the two resulting flaps 

 of body wall may be lifted and pinned so as to expose the abdom- 

 inal viscera (organs). It may also be necessary to clip oflF the 

 mesal portions of the two halves of the pectoral girdle in order 

 more clearly to reveal the relations of organs in the cephalic 

 part of the body cavity. In this study locate and identify all 

 structures mentioned, whether directed to do so or not. 



Note that the body cavity is lined by a smooth glistening mem- 

 brane, the 'peritoneum. The various organs are suspended from 

 the florsal walls by membranes called mesenteries. These are 

 double folds of peritoneum. 



The Heart. — With great care free the pectoral girdle from the 

 underlying muscles and blood ve.s.sels. Note the pericardial 

 cavity and examine the heart with a view to the identification of 

 the following parts: 



1. The thin-w.-dled auricles form the ceijhalic and dorsal divi- 

 sions of the heart. They are nameil according to their location 

 upon the right or left side. Blood returning from the several 



