190 ELEMENTARY BIOLOGY. [XIII. 



4. Raise the muscular wall of the abdomen and cut it in 

 the same way, slightly on one side of the middle line, 

 sufficiently to lay open the abdominal cavity, taking 

 great care to avoid the bladder which lies at the 

 posterior end of the cavity. Note the conspicuous 

 vein (anterior abdominal) which lies beneath the 

 muscles in the middle line of the belly. The liver, 

 stomach and intestines will be seen ; at the sides, in 

 the female, the ovaries and oviducts will be very con- 

 spicuous in the breeding season. Insert a small blow- 

 pipe into the cloacal opening: air blown in will 

 distend the large bilobed urinary bladder. If the 

 lungs are distended with air, one will be visible on 

 each side of the anterior end of the abdominal cavity, 

 and the extremity of the bristle passed into one of 

 them, through the glottis, will be seen. Lay open 

 the stomach to see the end of the probe passed into 

 the oesophagus. 



By turning the intestines on one side, the kidney, the 

 corpus adiposum and the testis (in the male) will be 

 exposed. Notice a number of small white patches on 

 each side of the vertebral column. They are accumu- 

 lations of calcareous crystals. 



5. In front of the liver, the apex of the heart will be seen 

 through the pericardium. Lay the latter open and 

 observe the position of the heart 



6. Cut away the left fore-limb and the left hind-limb, 

 with so much of the left half of the vertebral column 

 and skull as is needful to lay open the cavity which 

 contains the cerebro-spinal nervous centres. Pin the 

 frog in a dissecting dish on its right side, with suf- 

 ficient water to cover it, and 'study the position of the 



