XIII.] THE FROG, 19 



various organs in relation to a median longitudint 

 plane, making a careful diagram of the parts dif 

 played. 



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

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

 bones, make transverse sections (1) through the eye 



(2) through the centres of the tympanic membrane 



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

 half of the abdomen. Compare them •with the for( 

 going dissection. 



B. Dissection of the viscera in the ventral cavity. 



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

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

 beeswax, under water ; divide the skin along the al 

 dominal median line from the pelvis to the front of tl 

 lower jaw; next make a transverse incision at ea( 

 end of the longitudinal one, and then throw outwar( 

 the two flaps of skin thus marked out. The foUowii 

 points may now be noted. 



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

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

 shoulder. 



b. Some of the muscles of the abdominal wa 

 covered by a thin aponeurosis : through tl 

 lattfer can be seen — 



a. The rectus abdominis running from pelvis 

 sternum close to the middle line, and divid< 

 into a number of bellies by transverse tenc 

 nous intersections. 



/3. Other muscles outside the rectus on each sid 



