438 INTRODUCTORY. 



The tongue is always fleshy, and is attached to a bone called 

 the hyoid, suspended by ligaments to the cranium. 



The lungs are two in number, composed of an infinity of small 

 cells, and are always inclosed, without adhesion, in a cavity 

 formed by the ribs and the diaphragm, and lined by the pleura. 



The organ of voice is always at the superior extremity of the 

 trachea ; and a fleshy continuation denominated the velum palali, 

 or soft palate, establishes a direct communication between the 

 larynx and the back part of the nostrils. 



Living on the earth's surface, these animals are exposed to 

 the transitions of heat and cold. Their bodies have a covering 

 of hair, which is thicker in the northern regions, and more 

 scanty as they approach the warm latitudes. The Cetacea, how- 

 ever, which inhabit the sea, are totally devoid of this covering. 



The internal canal in the Mammalia, is suspended by a fold 

 in the peritoneum, called the mesentary, which contains a 

 number of conglobulated glands for the lacteal vessels. Another 

 production of the peritoneum, termed the epiploon, hangs on 

 the front of, and underneath the intestines. 



Cuvier divides the Mammalia into orders, whose essential 

 characters are founded on the construction of the feet or organs 

 of touch, and the number and kinds of teeth. On the perfec- 

 tion of the organs of touch, the power of expertness depends ; 

 and from the dentition may be ascertained, in a great measure, 

 the nature of their food and digestive functions. 



The organ of touch is more perfect in animals whose fingers 

 are more numerously developed, and which are least covered at 

 their tips ; — such as those possessing only a single nail protect- 

 ng their upper extremities, as in man ; sensation in the toes of 

 such as are covered with hoofs, on the contrary, is extremely 

 blunted. 



In the dentition given, and the generic characters, the method 

 of Cuvier is followed. The arrangement of the figures is in- 

 tended to represent the upper and under jaw. For example, in 

 man, the incisory, or cutting teeth, are in the centre of each 

 jaw, and are marked ^, (Plate III*, fig. 2 — 1,) that is, four above 

 and four below ; the canine, or sharp pointed teeth, are next to 

 these, and are marked j~{, (fig. 2 — 2,) that is, one on each side 

 of the incisory teeth in both jaws ; beyond these, and further 

 in the mouth, are the grinders, molars, er cheek teeth, marked 



