482 



HISTORY OF THE HUMAN BODY 



more highly developed olfactory sense than appears at present 

 (Fig. 131). 



Still another method for increasing the olfactory surface and 

 thus sharpening the scent seems to be found in the system of 

 accessory cavities, hollowed out in the surrounding bones and 

 communicating with one another and with the primary cavity. 

 These occur in the maxillary, sphenoid and frontal bones, and 

 in animals with the most elaborate nasal equipments are lined 

 with olfactory mucous membrane and may even develop tur- 

 binalia themselves. Some of these cavities are retained after 

 the loss of their olfactory function and are lined by simple 

 mucous membrane. The largest of these accessory cavities 



III IV 



FIG. 131. Lateral wall of human nasal cavity, showing the turbinals. 



(A) Embryo, after KILLIAN. (B) Adult, in part after WIEDERSHEIM. 

 I mx, maxilloturbinal ; II- VI, ethmoturbinals. 



in Man is the sinus maxillaris [antrum of Highmore~\ in the 

 maxillary bone; the frontal and sphenoid sinuses also belong 

 to the same system. [Cf. Fig. 130, C-F.] 



This extraordinary development of the organ of smell in 

 mammals is an illustration of the late perfection of a part that 

 has existed as a functional organ for a very long time, yet 

 without the necessity of a high degree of specialization. The 

 need of a turbinal is first felt in reptiles, but here a single one, 

 and that of the simplest pattern, is found to suffice. That the 

 human nose during its own past history once reached a much 

 higher state from which it has since failed through degenera- 

 tion and loss of the parts once gained is shown by the anlagen 



