234 SUMMARY. 



in shape in birds and very small in amphibia. The thalamus exists in the three 

 superior classes, it is smaller in birds than in mammalia, and very small in amphibia. 

 The soft commissure depends upon the presence of each thalamus ; there is a large 

 one in mammalia, but is placed more in the middle of the side of the thalamus 

 than in man ; it is very tough in the turtle. The anterior commissure exists in the 

 four, the posterior in the three, superior classes. There is a pineal gland in mammalia 

 and the turtle. The quadrigeininal bodies are distinct in mammalia, but vary, the 

 nates being either larger or smaller than the testes : they are solid at birth ; in birds 

 they are flattened and large, and have no distinction like that of the nates and 

 testes, and contain a ventricle in each communicating with the third ; they also exist 

 as hollow bodies without any anterior or posterior separation in amphibia and fishes. 

 The base of the brain is divided into lobes in man and simiae, and in the porpoise, 

 but in most others there is very little, if any, distinction ; the pituitary gland exists 

 in the four superior classes. Two distinct mammillary eminences exist in man, but 

 they are very generally conjoined in mammalia ; there is a prominence in birds ; 

 they do not exist in amphibia, they are however not only present but separate in 

 fishes. The cerebellum exists in the four superior classes ; in the invertebrate its 

 presence is doubtful ; it has large lateral lobes compared with the middle, and is large 

 in proportion to the size of the body in man and simite ; the lateral lobes compared 

 with the middle ones are smaller in mammalia generally ; it is convoluted throughout ; 

 in birds, it consists principally of a middle lobe, to which is attached on each side 

 a small one like the lobule appended to the lateral lobe of simiaB and other animals ; 

 it is convoluted, and has a ventricle ; in some of the amphibia, as the turtle, it is 

 hollow, and the parietes are thin, in several, it is a mere rudiment. In the cod, it 

 has a small ventricle, and consists principally of a middle lobe ; in the skate it has 

 a ventricle. The annular tubercle is largest in man, in mammalia it is proportioned 

 to the size of the crura of the cerebellum more than to the crura of the brain. The 

 trapezoid body exists in mammalia; it is composed of transverse fibres externally, 

 and internally of the tract of the larger portion of the intermediate layer of the 

 exterior region of the brain, after it has been joined by the tract of the first convo- 



