1516 THE STORY OF THE UNIVERSE 



ternal 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 tem- 

 poral 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 or- 

 bit, and sometimes a part of the cheek. In the em- 

 bryo state these bones also are much more subdivided. 



Their tongue is always fleshy, connected with a 

 bone called the hyoides, which is composed of sev- 

 eral pieces, and suspended from the cranium by 

 ligaments. 



Their lungs, two in number, divided into lobes 

 and composed of an infinite number of cells, are 

 always inclosed, 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 ex- 

 tremity of the trachea; a fleshy curtain, called the 

 velum palati, establishes a direct communication 

 between their larynx and nasal canal. 



Their residence on the surface of the earth render- 

 ing them less exposed to the alternations of cold and 

 heat, their tegument, the 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 long as is neces- 



