860 



HITCHCOCK'S ANATOMY 



Fig. 332. tiles constitutes but a very 



small part of the body. In 

 the frog the proportion to the 

 whole weight of the body is 

 as 1 : 172 ; in the Coluber 

 matrix (snake), 1 : 792 ; in a 

 turtle, 1 : 5688. The hemi- 

 spheres are smooth and hollow 

 internally. The optic lobes 

 are large in proportion to the 

 size of the eyes, and are hol- 

 low internally. The cerebel- 

 lum of frogs is merely a thin 

 plate of nervous matter. 



665. Nervous System of 

 Fishes— We find the lowest 

 development of the nervous 

 system among vertebrates in 

 the fishes. The brain here does not fill the whole cranial 

 cavity, so that between the brain and dura mater there is 

 found a quantity of loose cellular tissue, with w T hich is inter- 

 spersed a fluid oil. The brain in weight does not equal that 

 of the spinal cord, nor is it but a little broader than the cord. 

 Its weight in proportion to that of the body is about T j\ t th 

 part. It is composed of eight lobes, partly in pairs, and 

 partly unpaired behind one another, which seem to correspond 

 to the cerebellum (divided), corpora quadrigemina, thalami 

 optici, and medulla oblongata. 



666. Electrical Organs in Fishes. — There are at least 

 seven species of fish that possess the power of giving electric 

 discharges. The organs which accomplish this in the Torpedo 

 are two large crescent-like bodies (see Fig. 334), which are 



Brain of Turtle. A, Olfactive Ganglia. 

 B, Cerebrum. C, Optic Ganglia. D, Cere- 

 bellum. 



664. What is said of the brain of reptiles? State, its comparative size with that of the 

 whole body. 665. State some of the peculiarities of the brain in fishes. What is its 

 relative weight? 666. What is said of the electrical organs of some fishes? Give the 

 anatomy of these organs. 



