ITBR UK KM LAYER. 515 



<he ...,! , h has been effected in all \ .-rtebrateh 



ins.. tilings, a tecond function ha* been assumed I- 



time, to oondc 



fn-m ill.- "i-.il and i > h; i ryngeal cavities and tin- lung-. It IMS become 

 a kii.d of r'.xjx'nitary atriumfor the apparatus of respiration. The 

 assumption of this accessor \ t< ives a special stamp to 



; stages of the development of t lie organ, and is to be taken 



proper estimate of the course of the fur 



development is most of all determined by the tendency to an exten- 

 sive enlargement of the surface of the olfactory chamber. The 

 we of * !, does not affect the real olfactory 



mucous mei :l.rane or sensory epithelium, to \\\ 



nae. 

 It is therefore less connected wi-h an improvement of the sense of 



1 than with an anv. >ry fmietion in t he process of respirn ' 

 By an increase of the surface of the soft, vascular mucous membrane 

 the air that is swept over it becomes warmed and freed from part 

 of dust, which are caught by the in.>Nt Mirface. From this time 

 forward th. refore one inu>t di>i inu'uish a regio olfactoria and a regio 

 The former, which is derived from the sensory 

 epithelium of the original olfactory pit. ly small, 



ives the termination- ..f t he .,!;,. bory nerve, and is limited in the 

 Man to the region of the upper turbinal process and a part 

 of the septum nasi. 1 -n tliat cause- 



us which tho orgjin <>f ->iiM-ll attain- in the \. 

 Vertebrates. 



The iitrri-'isi' in tfte suri'iirf, of the nasal cavity is produced hv three 

 iiil.-rent events: (1) by the for: I the hard and soft palate, 



(_') hy the development of the turl.inal bones, (3) by the appearance 

 of the accessor of the nose. 



The lir>t evmt he^in> in Man toward t he m<l <>f the second li 



hen form, d on t!< y process 



(tig. i'^'.)) a i-idg.-, which projects mitive oral en 



and grows out hori/ontally The right and left palatal 



plates at iir>t embrace between them a broad fissure, through which 

 may he seen the original roof of the yand on this t 



v. Inch become more and more slit-like and are separated 

 l.y a bridge of suhMuiuv which has aris*-: he median frontal 



proce.xN and can lesignated as the nasal septum 



third month i tlfonure becomes gradually nanx 



