72 GENERAL ANATOMICAL CHARACTERS 



out to their destination. The cord is somewhat enlarged at the two 

 points where it gives off the great nerves to the anterior and the 

 posterior extremities, which, from their interlacements soon after 

 their origin, are called respectively the brachial and lumbar plexuses. 

 The ganglionic or sympathetic portion of the nervous system is well 

 developed, and presents few modifications. 



Sense of Touch. — The sense of touch is situated in the skin 

 generally, but is most acute in certain regions more or less 

 specialised for the purpose by the presence of tactile papilla?, such 

 as portions of the face, especially the lips and end of the snout, and 

 the extremities of the limbs when these are used for other purposes 

 than mere progression, and the under surface of the end of the tail 

 in some Monkeys. The " vibrissa? " or long stiff bristles situated 

 on the face of many mammals are rendered extremely sensitive to 

 touch by the abundant supply of branches from the fifth nerve to 

 their basal papilla?. In Bats the extended wing membranes, and 

 probably also the large ears and the folds and prominences of skin 

 about the face of some species, are so sensitive as to receive 

 impressions even from the different degrees of resistance of the air, 

 and so enable the animals to avoid coming in contact with obstacles 

 to their nocturnal flight. 



Taste and Smell. — The organs of the other special senses are 

 confined to the head. Taste is situated in the papilla? scattered on 

 the dorsal surface of the tongue. The organ of smell is present in 

 all mammals except the Toothed "Whales. It consists of a ramifica- 

 tion of the olfactory nerves over a plicated, moist, mucous 

 membrane, supported by folded plates of bone, placed on each side 

 of the septum nasi in the roof, or often in a partially distinct upper 

 chamber, of the nasal passage, so arranged that, of the air passing 

 into the lungs in inspiration, some comes in contact with it, causing 

 the perception of any odorous particles with which it may be 

 charged. Many mammals possess intense powers of smelling 

 certain odours which others are quite unable to appreciate, and the 

 influence which this sense exercises over the well-being of many 

 species is very great, especially in indicating the proximity of others 

 of the same kind, and giving warning of the approach of enemies. 

 The development and modification of the sense of smell is probably 

 associated with that of the odorous secretion of the cutaneous 

 glands. 



Sight. — The organ of sight is quite rudimentary, and even 

 concealed beneath the integument, in some burrowing Rodents and 

 Insectivores, and is most imperfectly developed in the Platanista, or 

 Freshwater Dolphin of the rivers of India. In all other mammals 

 the eyeball has the structure characteristic of the organ in the 

 higher Vertebrata, consisting of parts through which the rays of 

 light are admitted, regulated, and concentrated upon the sensitive 



