Comparative Anatomy of the Brain. 599 



while the posterior lobe of the cerebrum and its contained posterior 

 cornu and hippocampus minor are more or less rudimentary. In all the 

 other Apes, Marmosets and Baboons, these parts are all well developed, 



FIG. 338. Vertical middle section 

 of Brain o/ Orany Outang X %. 

 1. Superior longitudinal com- 

 2 Corpus Callqsum. [ missure. 

 3. Septum Lucidum. 

 4. Fornix. 

 5. Optic Thalamus. 

 6. Pituitary gland. 

 7. Corpora Quadrigemina. 

 8. Crura Cerebri. 

 9. Cerebellum. ( Vrolik.) 



and in some cases as well or 

 better than in man. (Huxley. ) 



There is, in fact, in the 

 Quadrumana alone sufficient 

 difference in brain structure * FlG 338 



to split the family in two and put a part of it among the Lissencephala, 

 alongside the rodents and insectivores, and promote the rest to a sub- 

 class separate from the Dog and the Pig, provided the development of 

 convolutions is made the basis of the classification. 



The average weight of brain to the body in fishes is as 1 to 3, 000. 

 In a Chub ( Luciscus Cyprinus ) weighing 842 scruples, the brain, ex- 

 clusive of olfactory lobes, weighed one scruple. In a Carp ( Cyprinus 



FIG. 339. Upper surface of Brain of 

 Orang Outang. (After Sandifort.) 



Carpio) of 11,280 grains 

 weight, the brain weighed 14 

 grains. In a Lamprey of 750 

 grains the brain weighed half a 

 grain. The brain of the fish, 

 attains its mature size before 

 the rest of the body. In the 

 Newt weighing 39 grains, the 

 brain weighs one-seventh of a 

 grain, and in the Sirens, Am- 

 phiumes and Menapomes the 

 proportion of the brain to the 

 body is less than in the case of the Newt. The average weight of the 

 brain to the whole body in the mammalia is said to be as 1 to 186, that 

 of birds as 1 to 212, reptiles, I to 1321, fishes, 1 to 5668. But there 

 are great differences between the different members of the classes. 

 Thus the Blue-headed Tit has a brain one-twelfth as heavy as its body, 

 or three times as heavy as man's brain relatively. The brain of the 

 Goldfinch is to his body as 1 to 24, that of the field Mouse, a mammal, 

 as 1 to 31. The relatively large brain of these animals is probably due 



FIG. 339. 



