

XIII.] THE FROG. 191 



various organs in relation to a median longitudinal 

 plane, making a careful diagram of the parts dis- 

 played. 



7. In a frog which has lain in bone-softening solution (say 

 1 per cent, chromic acid) sufficiently long to soften the 

 bones, make transverse sections (1) through the eyes, 



(2) through the centres of the tympanic membranes, 



(3) through the shoulder-girdle, (4) through the hinder 

 half of the abdomen. Compare them with the fore- 

 going dissection. 



B. DISSECTION OF THE VISCERA IN THE VENTRAL CAVITY. 



1. Lay a frog, which has been killed with chloroform, on 

 its back and pin it out on a layer of paraffin or 

 beeswax, under water ; divide the skin along the ab- 

 dominal median line from the pelvis to the front of the 

 lower jaw ; next make a transverse incision at each 

 end of the longitudinal one, and then throw outwards 

 the two flaps of skin thus marked out. The following 

 points may now be noted. 



a. A great vein (musculo-cutaneous) on the under sur- 

 face of each flap of skin, about the level of the 

 shoulder. 



6. Some of the muscles of the abdominal wall, 

 covered by a thin aponeurosis : through this 

 latter can be seen 



a. The rectus abdominis running from pelvis to 

 sternum close to the middle line, and divided 

 into a number of bellies by transverse tendi- 

 nous intersections. 



/3. Other muscles outside the rectus on each side. 



