356 



THE BOOK OF THE CAT. 



other situations on the cat's body where it 

 may be felt, but to find the exact point 

 requires some intimate anatomical knowledge. 

 The temperature, or normal heat, of the body 

 of the cat is 100 F. ; it may, however, be 

 slightly above or below this. 



The brain of the cat, following the general 

 structure of the higher mammals, is divided 

 into very similar areas or divisions. The 

 larger or more anterior portion is called the 

 cerebrum (Fig. I., A), and is divided into right 

 and left hemispheres. Its surface is divided into 

 convolutions or gyri (E) by certain shallow 

 fissures, which have received specific names. 

 Very intimately attached to the under-surface 



In all the higher mammals the eye can 

 accommodate itself to the varying influence of 

 light. This is mainly done by means of the 

 central black part or pupil (Fig. ix., A). The 

 pupil is merely a hole in the iris, or coloured 

 part of the eyeball (B), and it is by its contrac- 

 tion or expansion that the exact amount of light 

 necessary is admitted to act upon the sensitive 

 retina at the back of the eye. The form of the 

 pupil varies considerably in different animals. 

 In the cat's eye during bright sunshine it is 

 reduced to a thin vertical line ; at dusk it 

 expands to a nearly circular form. This ver- 

 tical reduction is by no means common to the 

 entire cat family. In very many species the 



AT DAY-TIME. 

 A. Contracted linear pupil. 

 B. Iris. [nans). 



C. Nictitating membrane (Plica semilu- 

 D. Opening of the Harclerian Gland Duct. 



FIG. IX. THE CAT'S EYE. 



AT NIGHT-TIME. 



A. Expanded and nearly circular pupil. 

 B. Iris. 



C. Nictitating membrane. 

 D. Opening of Harderian Duct. 



C. C'at'seye, showing the third 

 eyelid or nictitating mem- 

 brane fully extended. 



of this part of the brain are the olfactory lobes 

 (D), in which are situated certain nerves con- 

 cerned in the sense of smell. The hinder and 

 smaller part of the brain is called the cere- 

 bellum (B), and is much darker in colour than 

 the cerebrum. Its surface is made up of 

 numerous small foldings of its substance, 

 which, on section, look like the branches of 

 a small tree ; these branches finally fuse and 

 terminate on the under-side of the base of 

 the brain. 



Intimately associated in a most complex 

 manner with the cerebrum and cerebellum is 

 the medulla oblongata (c), an enlarged part of 

 the spinal cord. The brain of the cat, it may 

 be remarked, is not nearly so highly organised 

 as that of the dog. 



pupil retains a rounded form even when con- 

 tracted to its minimum. 



On the inner angle of the cat's eye there 

 is a curious semi-transparent fold of skin, 

 called by naturalists the plica semilunaris, or 

 nictitating membrane. In reptiles and birds 

 this is a very important factor in the preserva- 

 tion of the eye from external injuries, and it 

 acts also as a regulator of the admission of 

 light. It is well developed in nocturnal 

 reptiles and birds, and as the cat's ancestors 

 were doubtless more nocturnal than they are 

 now, it probably was in active use. It is, 

 however, useless now, the cat having no control 

 over it. It is one of many interesting vestigial 

 structures the cat carries about with it of its 

 former ancestry from a lower-organised animal. 



