34 THE FROG CHAP, n 



the region of the kidneys and examined under water (com- 

 pare Fig. 5). 



Sketch the contents of the abdomen in situ. 



The Neural Cavity and its Contents. Now turn the 

 frog with its back upwards, and pin it firmly to the bottom 

 of the dissecting-dish or to the dissecting-board as before. 

 Pinch up the skin, make a longitudinal cut through it from 

 the snout to within a short distance of the vent, and turn 

 the flaps right and left. The muscles of the back will be 

 exposed, and, in front, the roof of the skull, which lies just 

 beneath the skin. Carefully dissect away the muscles along 

 the middle line of the back until the vertebral column is 

 seen. Compare a prepared skeleton and Fig. 8, and make 

 out the arches of the vertebra?. Between the first of these 

 and the back of the skull is a slight space : insert one blade 

 of the strong scissors into this, directing the point backwards, 

 and cut through the arch of the first vertebra, first on one, 

 then on the other side, and finally detach and remove the 

 little piece of bone. The neural canal will then be exposed, 

 in which lies the spinal cord, ending behind in a thread-like 

 prolongation (compare Fig. 6) : work backwards, cutting 

 away the arches of the remaining vertebrae. 



Next, using the scissors in the same manner, cut away, 

 bit by bit, the roof of the skull : two large bones ihefronto- 

 parietals (see Figs. 8 and 9), forming a considerable part of 

 the roof, can be more easily removed by raising them up 

 with the edge of a scalpel. Note the cavity of the skull and 

 its contained brain. 



General Structure of the Limbs. With a strong knife, cut 

 across one of the legs at about the middle of the thigh. 

 Compare p. 28, and notice the thigh-bone, muscles, and 

 skin. Sketch. 



Now preserve your specimen in formaline (about 2 per 

 cent.) or spirit (70 per cent.). 



