556 THE BABBIT 



CHAP. 



H. The Eye. 



On account of its larger size, it is better to substitute 

 the eye of an ox or sheep which can be obtained fresh from 

 a butcher for that of the rabbit. Two specimens should be 

 obtained, and the fat, muscles, and any portions of the 

 eyelids remaining attached cleared away. Dissect under 

 water. 



1. After noting the conjunctiva, cornea, sclerotic, optic 

 nerve, iris, and pupil, insert the scissors into the margin of 

 the cornea, and cut round and remove it so as to expose 

 the aqueous chamber, noting the aqueous humour, as well as 

 the iris, lens, and pupil (compare Fig. 57). Sketch. 



Insert the handle of a scalpel between the iris and sclerotic 

 and separate off the latter from the choroid around the outer 

 half of the eyeball, first making four radial cuts in the 

 sclerotic, beginning at its margin, at equal distances from one 

 another. Turn back the four flaps thus made, and insert 

 pins through them so as to fix the eye firmly down under 

 water with the iris uppermost : note the ciliary muscle around 

 the outer margin of the iris, the choroid, and the ciliary vessels 

 and nerves. Then make two radial cuts, a short distance from 

 one another, through the iris, and turn back the portion 

 between the cuts, noting the radially arranged ciliary 

 processes. Sketch. 



Cut through the choroid and the parts enclosed by it, 

 horizontally, around the line up to which it has been already 

 exposed, so as to separate the eyeball into an inner and outer 

 hemisphere : in doing so, the gelatinous vitreous humour 

 must be cut with the scissors. Examine and sketch both 

 sections, noting in the outer hemisphere the retina, stopping 

 short at the outer margin of the ciliary processes, and the lens 

 with its capsule ; and in the inner hemisphere the retina 

 with its blood-vessels, and the blind-spot (or point of entrance 

 of the optic nerve). Then remove the retina and observe 

 the choroid with its iridescent tapetum. 



2. Cut your second specimen into vertical halves with the 

 scissors, making the cut pass through the cornea, pupil, 

 and optic nerve. As it is difficult to cut through the lens 

 without disturbing its relations, it should be carefully 

 separated from one half, and left entire on the other half. 

 Examine the relations of the parts once more, compare 

 Fig. 57, and sketch. 



/. Dissection of typical flexor and extensor muscles and 

 joints of the fore-limb. 



i. Expose the biceps (chief flexor of the fore-arm). Its 



