298 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



man and the higher mammals the surface of the forebrain is 

 thrown into many convolutions; among the lowest the surface 

 is smooth. Of the organs of special sense, those of touch con- 

 sist of free nerve-endings or minute tactile corpuscles in the 

 skin. The tactile sense is especially acute in certain regions, 

 as the lips and end of the snout in animals like hogs, the fingers 

 in man, and the under surface of the tail in certain monkeys. 

 All the other sense-organs are situated on the head. The or- 

 gans of taste are certain so-called taste-buds located in the 

 mucous membrane covering certain papillae on the surface of 

 the tongue. The organ of smell, absent only in certain whales, 

 consists of a ramification of the olfactory nerves over a moist 

 mucous membrane in the nose. The ears of mammals are 

 more highly developed than those of other vertebrates both in 

 respect to the greater complexity of the inner part and the 

 size of the outer part. A large outer ear for collecting the 

 sound-waves is present in all but a few mammals. A tympanic 

 membrane separates it from the middle ear in which is a chain 

 of three tiny bones leading from the tympanum to the inner 

 ear, which is composed of the three semi-circular canals and 

 the spiral cochlea. The eyes have the structure characteristic 

 of the vertebrate eye, consisting of a movable eyeball com- 

 posed of parts through which the rays of light are admitted, 

 regulated, and concentrated upon the sensitive expansion, 

 called retina, of the optic nerve lining the posterior part of 

 the ball. The eye is protected by two movable lids. In 

 almost all mammals below the Primates (man and the 

 monkeys) there is a third lid, the nictitating membrane. In 

 some burrowing rodents and others the eye is quite vestigial 

 and even concealed beneath the skin. 



The mental qualities of animals reach their highest develop- 

 ment among the mammals. In the wary and patient hunting 

 for prey by the carnivora, the gregarious and altruistic habits 

 of the herding hoofed mammals, the highly developed and 

 affectionate care of the young shown by most mammals, and 

 in the loyal friendship and self-sacrifice of dogs and horses 

 in their relations to man, we see the culmination among animals 

 of the development of the functions of the nervous system. 



