650 TEXTBOOK OF ZOOLOGY 



Nervous System 



The nervous elements of the cat, as of most vertebrates, form sys- 

 tems, known as the central, peripheral, and autonomic (sympathetic). 

 The first includes the brain and spinal cord and is protected by three 

 membranes called meninges. The outer one is the dura mater, under 

 it the arachnoid, and on the surface of the nervous tissue, the pia 

 mater. The j)eripheral system includes twelve pairs of cranial nerves 

 emanating from the brain, and about forty pairs from the spinal 

 cord. The autonomic system is composed of two trunks which bear 

 ganglia and extend one on each side of the vertebral column through 

 its length of the trunk. Branches from these trunks reach all vis- 

 ceral organs. 



The hrain presents a much enlarged cerehrum with fairly well- 

 developed convolutions. It has spread until the diencephalon and 

 midbrain have been covered by it. The cerebellum, which is also 

 quite well developed, is divided into two lateral hemispheres and a 

 convoluted, central vermis (Fig. 352). 



The sense organs are relatively well developed. The olfactory 

 organ is located in the deep posterior portion of the nasal cavity, 

 which is quite large. The sense of taste is located in the vallate 

 papillae and in some fungiform papillae on the dorsal surface of the 

 tongue, as well as sparsely scattered in the mucous membrane of the 

 mouth and pharynx. The ear, an organ of hearing, is composed of 

 the pinna, or external ear, which directs sound waves to the tympanic 

 membrane, from which they are transferred by three bony ossicles to 

 the vestibule of the spiral-shaped cochlea. The latter contains the 

 sensory organ of Corti of the inner ear. The eye is of typical ver- 

 tebrate form and is developed for keen vision. 



Excretory System 



The kidneys, two ureters leading from the kidneys, the bladder, 

 and the urethra constitute the principal organs of this system. Each 

 kidney is composed of an outer cortical layer about one-half centi- 

 meter thick and an inner medidlary substance. In the cortical sub- 

 stance are hundreds of renal corpuscles, each composed of a ball of 

 capillaries, the glomerulus, and an epithelial wall, Bowman's capsule. 

 Urine is taken from the blood here and carried through the parts of 

 the uriniferous tubules to the pelvis of the ureter embedded in the 



