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 papille, 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 “vibrisse” 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 papille 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 
