TO MAMMALS. JX 



long immersed in water, some arteries appearing to be intended as 

 reservoirs of arterial blood, and dilatations of some of tbe veins 

 prevent too great distension v^hile the respiration is stopped. 



The brain is larger than in any other class of animals, owing 

 chiefly to the increased size of the cerebral hemispheres, which are 

 united in most by a fibrous band called the corpus callosum. The 

 cerebellum too has lateral lobes which are united by the pons varolii, 

 and the hemispheres are usually convoluted externally. The Mar- 

 supial animals however do not possess the great commissures, and the 

 cerebrum is smooth externally, thus more resembling Birds. The 

 olefactovy tubercles, and the optic lobes, are greatly reduced in size. 



The organs of the senses are highly specialized, and in a great 

 state of perfection in Mammals. The sense of touch is very deli- 

 cate, and is usually concentrated in various parts, e. g,, in the 

 whiskers of the Seals, of some Insectivora and Carnivora, in the lips 

 of the Horse, the trunk of the Elephant; and this sense is greatly 

 developed and extended among Bats in every part of the body, but 

 especially in the naked wrings, the ears and facial appendages. 



The sense of smell is very acute in most animals, and many have 

 a mobility of the outer nostrils to aid it, never found in the other 

 Vertebrata. The olefactory tubercles are so diminished in size as 

 barely to be recognized. We are all familiar with the power of the 

 scent in the Dog, as well as in most of the Carnivora, which enables 

 them to discover and hunt down their prey. Antelope, Deer and 

 other timid animals have likewise very acute sense of smell, to en- 

 able them to avoid approaching danger. The nasal plates of the 

 ethmoid bone, and the convolutions of the turbinated bones are coated 

 with a delicate membrane, which forms a large surface, amply sup- 

 plied with minute branches of the olefactory nerves, and the air 

 inhaled passing to the lungs over this membrane imparts the im- 

 pression. 



The structure of the eye is in all Mammals almost identical with 

 that in Man. In some the pupil is round, in others oblong or linear. 



In Bats, and some nocturnal Insectivora, the external eye is very 

 minute, but the sense of sight appears to be compensated for by an 

 increase of that of touch. Many of the E/uminants have the. eye 



