Practical Course. 93 
(2) In front of the cerebellum a pair of large rounded nerve-masses 
(optic lobes), which supply the eyes. 
(3) In front of the optic lobes a pair of smaller closely appressed 
nerve-masses (cerebral hemispheres). From the cerebral 
hemispheres a pair of nerves are given off which com- 
municate with the smal] olfactory lobes in front. These, 
however, are very liable to be obliterated in rough dis- 
secting. 
Dissect off the muscles down the back and cut away the dorsal spines 
and arches with scissors, so as to expose the spinal cord. Trace it back- 
wards as far as the specimen admits. Then sketch the dissection, 
Lift up the spinal cord carefully with forceps and turn the whole 
brain forwards, so as to be able to examine its ventral surface. Make 
out i— $ 
(1) The numerous nerves which leave the ventral surface of the 
medulla oblongata on either side, 
(2) The pair of large optic nerves, which place the eyes in com- 
munication with the optic lobes. 
(3) The paired bean-shaped nerve masses (lobi inferiores) situated 
immediately underneath the optic lobes. They enclose 
between them a small dark-coloured nerve-mass known 
as the pituitary body. 
DISSECTION OF THE FROG. 
Frogs are excessively common in Dehra in every pool of water. 
They can be easily caught with a small hand-net. The largest available 
specimens should be procured for dissection. If possible, some tadpoles 
(immature frogs) also should be obtained, to sbow the gill-breathing 
stage through. which the Amphibia pass. The largest species of frog in 
Dehra is the Bull-frog (Rana digrina), and the following description 
therefore is taken from this species, Any of the other forms, however, 
will do almost equally well, though they are somewhat more difficult to 
dissect on account of their smaller size. Frogs are kuown locally as 
maindak, 
Any number of frogs can be killed in a few minutes by putting 
them into an earthen pot (gumla), closing up the top witha dissecting 
dish and pouring in a little chloroform. 
Examine a specimen and notice the blunt head in front, the thick- 
set body behind, and the two pairs of jointed limbs, the whole being 
clothed with smooth moist skin, 
Notice that the specimens are of two kinds :— 
(1) Males, with bag-like infoldings of the skin (vocal sacs) on 
either side of the lower jaw. 
