24O THE EVOLUTION OF MAN. 



pharynx may be entered without touching the cavity of the 

 mouth. This is the passage by which air is usually inhaled; 

 the mouth being shut, it enters the pharynx, and thence 

 passes through the windpipe into the lungs. Both nasal 

 cavities are separated from the mouth-cavity by the hori- 

 zontal bony palate roof, to the back of which the soft 

 palate and the uvula is attached, like a hanging curtain. 

 In the upper and hinder portion of both nasal cavities the 

 olfactory nerve extends over the mucous membrane, which 

 lines these parts. This is the first pair of brain nerves, 

 which issue from the skull-cavity through the sieve bone. 

 Its branches extend partly over the partition wall, and 

 partly over the inner side-walls of the nasal cavities, to 

 which are attached the "shells," or spongy bones of the 

 nose complex bony structures. These " shells " are much 

 further developed in many of the higher Mammals than 

 in Man. In all Mammals there are three of these " shells " 

 in each of the two nasal cavities. The sensation of smell 

 is produced by a current of air, containing odorifei'ous 

 matters, passing over the mucous membrane of the cavities, 

 and there corning in contact with nerve-ends. 



The peculiar characters which distinguish the olfactory 

 organ of Mammals from that of lower Vertebrates, are 

 represented in Man. In all specific points the human nose 

 exactly resembles that of the Catarhine Apes, some of which 

 indeed possess an entirely human external nose (see face 

 of the Nose-ape, Fig. 202, p. 175). The first rudiment of the 

 olfactory organ in the human embryo does not, however, 

 show any signs of the fine form of the future catarhine 

 nose. Indeed, it first appears in the same form which 

 persists for life in Fishes ; in the form of two simple pits, 



