THE FROG 95 



carefully the points where the skin is attached to the muscles. 

 Note the large blood vessels on the inner surface of the skin ; 

 these are the cutaneous veins and arteries. The blood is brought 

 to the skin to be aerated, an important part of the respiration of 

 the animal being carried on through the skin. 



Through the semitransparent muscles in the region of the 

 forelegs may be seen and felt a number of platelike bones and 

 cartilages. These form the pectoral (shoulder) girdle and the 

 breastbone, which support the fore limbs. In the midventral line 

 will be seen through the body wall a broad dark line; this is 

 the abdominal vein. 



Observe the arrangement of the ventral body muscles; see 

 page 79. 



Lift up the ventral body wall with forceps, and with scissors 

 make a longitudinal incision through it in the median line the 

 length of the body. Pull the two flaps of the body wall gently 

 apart and pin them. Examine the organs which lie in the ab- 

 dominal cavity, but without disturbing any of them. 



If the animal is a male, or a female which is not breeding, the 

 most conspicuous organs will be the large reddish liver and the 

 intestine. If it is a mature female, the dark-colored granular 

 ovaries may occupy a large part of the space within the body 

 cavity; in this case the ovaries should be removed with the aid 

 of forceps, so that the other organs can be studied. 



Lying on the left side of the liver and wholly or partly con- 

 cealed by it is the elongated stomach. In front of the liver in the 

 median line is the conical heart within its membranous pericar- 

 dium. Lying between the lobes of the liver may be seen the small, 

 greenish, spherical gall bladder. - 



Make a transverse incision in each flap of the body wall. Turn 

 the flaps to the side and pin them down, exposing fully the internal 

 organs. 



In addition to the organs already mentioned one or both lungs 

 may be seen. They are usually shriveled, saclike organs which 

 lie at the forward end of the abdominal cavity, concealed by the 

 liver. If either is full of air, it should be punctured and made 

 to collapse. At the hinder end of the abdominal cavity, between 



