Mammalia: Nervous System 679 



The mouth and nasal cavities have a wide avenue of communica- 

 tion via the posterior region of the pharynx (Figs. 171, 469). Gas from 

 the mouth and pharynx may pass up and around the rear edge of the 

 soft palate into the nasopharynx. While food is in the mouth, and 

 especially while it is being chewed, vapors from the food may be drawn 

 into the current of exhaled air and thus carried forward through the 

 nasal passages, enough of it penetrating into the olfactory region to 

 cause olfactory stimulation. In man, at least, taste is probably limited 

 to the sensations which we describe as sweet, sour, salty, and bitter. 

 Those qualities which we describe as the "flavors" of food — the charac- 

 teristic taste of a peach as distinguished from that of a pear, irrespec- 

 tive of the fact that both are sweet — are sensed only through the nasal 

 olfactory epithelium. The sugar in the drink is tasted, the coffee is 

 smelled. Knowing that the food is in the mouth, we thoughtlessly 

 assign the location of the receptors to the region of taste. The human 

 "palate" gets credit for a vast amount of work which is really done 

 by the nose. The flavors of food are strongly sensed only during exhala- 

 tion; during inhalation it has little or no flavor. When the nostrils are 

 held tightly shut, apple and onion taste much alike, or not at all. The 

 anatomic relations of the alimentary and nasal passages of land mam- 

 mals are so similar to those of man as to make it highly probable that, 

 for most mammals, "taste" is largely a matter of smelling — and it is 

 even more probable that they give little thought to the location of 

 the receptors. 



Nose, Snout, Trunk 



With increase in importance of the mammalian nasal apparatus, 

 the nasal region of the head builds up dorsally and protrudes forward 

 beyond the upper jaw and lip, thus producing a characteristic mam- 

 malian feature. Moderately developed, it is the snout of most mam- 

 mals. It attains the extreme of exaggeration in the elephant's trunk 

 and appears in varying degree of refinement in the human nose. The 

 snout is especially prominent in hogs and becomes elongated into a 

 veritable proboscis in the tiny elephant-shrew (an insectivore: Fig. 

 508), in the ungulate tapir (Fig. 565), the male elephant-seal (a carni- 

 vore), and in the proboscis-monkey of Borneo. The powerfully muscu- 

 lar trunk of the elephant is an extraordinary organ in that it combines 

 the functions of prehension and breathing. The external nares are at 

 its tip. The olfactory regions of the nasal passages are well back in the 

 head, posterior to the base of the trunk. These various forms of I lie 

 snout receive more or less skeletal support at their basal regions by 

 elongation of the nasal bones and by cartilages developed anterior to 

 the nasal bones. 



