MAMMALIA. 33 



cavity formed by the ribs and diaphragm and, lined by the pleura ; the 

 organ of voice is always at the upper extremity of the trachea ; a fleshy 

 curtain., called the velum palati, establishes a direct communication, 

 between their larynx arid nasal canal. 



Their residence on the surface of the earth rendering them less ex- 

 posed to the alternations of cold and heat, their body is but moderately 

 covered with hair, and in such as inhabit warm climates, even this 

 slight covering is somewhat rare. 



The Cetacea, which live exclusively in water, are the only ones that 

 are altogether deprived of it. 



The young are nourished for some time after birth by milk, a fluid 

 peculiar to animals of this class, which is produced by the mammae at 

 the time of parturition, and remains as long as it is necessary. It 

 is from the mammae that this class derives its name; and being a 

 character peculiar to it, they distinguish it better than any other 

 external characteristics. . ,r 



DIVISION OP THE MAMMALIA INTO ORDERS. 



The variable characters which form essential differences among the 

 Mammalia are taken from the organs of touch, on which depends their 

 degree of ability or address, and from their teeth, which determines the 

 nature of their aliment ; and are all closely connected, not only with 

 every thing relative to the functions of digestion, but also with a multi- 

 tude of other differences relating even to their intelligence. 



The degree of perfection in their organs of touch is estimated by the 

 number and the pliability of the fingers, and from the greater or less 

 extent to which their extremities are enveloped by the nail or the 

 hoof. 



A hoof which completely envelopes the end of the toe, blunts its 

 sensibility, and renders the foot incapable of seizing. 



The opposite extreme is when a nail, formed of one single lamina, 

 covers only one of the faces of the extremity of the finger, leaving the 

 other possessed of all its delicacy. 



The nature of the food is known by the grinders, to the form of 

 which the articulation of the jaws universally corresponds. 



To cut flesh, grinders are required to be as trenchant as a saw, and 

 jaws fitting like scissors, having no other motion than a vertical one. 



For bruising roots or grains, flat-crowned grinders are necessary, and 

 jaws that have a lateral motion ; in order that inequalities may always 

 exist on the crown of these teeth, it is also requisite that their sub- 



D 



