864 



COMPARATIVE ANATOMY 



taste is almost as poorly developed as the olfactory sense. The inner ear,, 

 especially the cochlea, is more complex than in reptiles. The eye of 

 birds is large and highly organized, probably keener than that of any 

 other animal. Sclerotic plates cover the eyeball. A fan-shaped pecten 

 (Fig. 490) of unknown function is inserted in the vitreous humor. 



A. c. 



Fig. 485. 



Nerve end-organs. A, longitudinal section of tactile papilla, containing a Meissner'* 

 corpuscle. B, Section through a terminal corpuscle (end-bulb of Krause) from the conjunctiva, 

 C, Section of a Pacinian corpuscle. The nerve fiber, n,m, enters the capsule through the channel 

 /, and has its terminal branches at a. (A, C, from Ranvier, B, from Dogiel.) 



MAMMALIA 



It seems that some of the archaic mammals did not have a more 

 highly developed brain than reptiles. Modern mammals, however, 

 especially the higher groups, have a brain that is much more highly de- 

 veloped than that of all other forms. 



In these higher groups the brain is relatively large (Figs. 472, 484) r 

 the cerebral hemispheres showing the greatest increase. The increase 

 is practically confined to the pallium (neopallium). 



There is an elaborate system of commissures to connect the two 

 sides of the brain, the corpus callosum being the most important. In 

 fact, the corpus callosum is largest in the highest groups. 



In the lower animals the olfactory lobes lie at the tip of the cere- 

 brum, but in the higher forms the pallial increase pushes the frontal 

 lobes forward so that the olfactory lobes are brought to the lower sur- 

 face and are separated from the cerebrum proper by a rhinal fissure on 

 each side. 



The olfactory tract and the hippocampal tract connect the olfactory 

 lobes with regions farther back, but in man the hippocampal tract is 

 largely rudimentary, the corpus callosum acting as the great connecting 

 region. 



The great numbers of fibers from the increased pallium form the 

 corona radiata which connects the cortex with the more posterior por- 

 tions of the brain. And, as connection is made through the thalami, the 

 thalamic regions become greatly enlarged, extend into the third ven- 

 tricle and reduce that to a mere slit. Where the two walls come in con- 

 tact the intermediate mass is developed. 



The mesencephalic lobes are four in number, now called the corpora 



