MAMMALIA. 121 



optic tract, and at the base of the brain its conjunction with the large prominence 

 giving origin to the olfactory nerve is again seen. In the rat, the great commissure is 

 very small, but the fornix and hippocampus are so large as to occupy nearly the whole 

 lateral ventricle. 



The striated bodies and thalami are nearly the same as in man ; they are small in 

 the porpoise in proportion to the size of the brain ; in all an anterior, posterior, and 

 soft commissure exist. The taania, or medullary line, is situated between the striated 

 body and thalamus. 



The pineal gland is found in the same situation as in man : it varies in shape, and 

 has processes extending forwards to the thalami, and backwards to the nates. There 

 is a considerable variety in the proportion of the nates and testes to each other. In the 

 baboon, the nates are much larger than the testes ; in other simia3, the nates are nearly 

 round, but rather flattened at the top, and not much larger than the testes. In the 

 pig, and in herbivorous animals, the nates are much larger than the testes, as in the 

 sheep and horse, and in the carnivorous the testes are the largest. In the jaguar, the 

 common cat and dog, the surface of the nates is broader and flatter than that of the 

 testes, but these are more prominent, and extend further laterally, and the geniculate 

 bodies are large. In the rat, the nates are longer, but less broad than the testes. In 

 the porpoise the nates are red, the testes white and larger than the nates. 



The striated body is large throughout the class in proportion to the brain. In 

 the horse and ox it is long, but not quite so wide at the anterior part as in man. 

 On removing the grey matter and the white fibres passing through it, the internal 

 oval receptacle is left ; it is less capacious and more shallow than in man, and on 

 removing the low convolutions at the bottom of the fissure of Sylvius, or in their 

 corresponding place, a similar cavity remains as in man, but not so extensive. The 

 anterior commissure becomes connected with the anterior crus of the fornix, and on 

 leaving it passes towards the middle lobe of the brain in simise as in man to the group 

 of low convolutions forming the island ; it divides, when one portion becomes connected 

 with the tract of the low convolutions at the anterior lobe of the brain, whilst the 

 other is attached to the more posterior of the same group at the middle lobe. In the 



R 



