MAMMALIA. 43 



complete the cranium, the second to close the labyrinth of the ear, 

 the third to form the parietes of the tympanum, &c. These bony 

 portions, still more numerous in the earliest period of the fcetal ex- 

 istence, are united more or less promptly, according to the species, 

 and the bones themselves finally become consolidated in the adult. 



Their face consists of the two maxillary bones, between which pass 

 the nostrils; the two intermaxillaries are situated before, and the two 

 ossa palati behind them; between these descends the vomer, a bony 

 process of the os ethmoides; at the entrance of the nasal canal are 

 placed the ossa nassi; to its external parietes adhere the inferior 

 turbinated bones, the superior ones which occupy its upper and pos- 

 terior portion belonging to the os ethmoides. The jugal or cheek 

 bone unites the maxillary to the temporal bone on each side, and 

 frequently to the os frontis; finally, the os unguis, and pars plana of 

 the ethmoid bone occupy the internal angle of the orbit, and some- 

 times a part of the cheek. In the embryo state these bones also 

 are much more subdivided. 



Their tongue is always fleshy, connected with a bone called the 

 hyoides, which is composed of several pieces, and suspended from 

 the cranium by ligaments. 



Their lungs, two in number, divided into lobes, and composed of 

 an infinitude of cells, are always enclosed, without any adhesion, in 

 a 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 com- 

 munication between their larynx and nasal canal. 



Their residence on the surface of the earth rendering them less 

 exposed to the alternations of cold and heat, their tegument (hair) 

 is but moderately thick, and in such as inhabit warm climates, even 

 that is 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 a fluid (milk) 

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

 at the time of parturition, and continues to be so as long as is necess- 

 ary. It is from the wiamwKB that this class derives its name, and 

 being a character peculiar to it, they distinguish it better than any 

 other that is external. 



