512 



EMBRYOLOGY. 



The study of the development of the orpin of smell acquires 



additional interest, when 

 one takes into account 

 the comparative - ana- 

 tomical conditions. It 

 is then found that the 

 various stages through 

 which the organ <>t' >moll 

 passes during embryonic 

 life, in Mammals for 

 example, have been 

 preserved as permanent 

 conditions in 1 o w r 

 classes of Vertebi 

 Thus in tho case <>t 

 many groups of Fi>ln-s 

 the organ of smell is 

 preserved, as it were, in 

 its initial stage in the 

 form of a pair of pits. 

 Upon closer histological 

 investigation, however, 

 this condition ocquin s 

 a special interest, be- 

 cause it presents points of comparison with simple)' sensory organs 

 u'hich are distri- 

 buted over tJie in- 

 tegument. As 

 BLAUE especially 

 has shown in a 

 meritorious work, 

 the olfactory 

 nerve does not 

 terminate in this 

 case in a con- 

 tinuous olfactory 

 epithelium, but in 

 individual. >h a rply 

 differentiated or- 



Fig. 286. Frontal reconstruction of the oro-pharyngeal 

 cavity of a human embryo (Rg of His) 11*5 mm. long, 

 neck measurement. From His, " Menschliche Em- 

 bryonen." Magnified 12 diameters. 



The upper jaw is seen in perspective, the lower jaw in 

 section. The posterior visceral arches are not visible 

 from the outside, since they have moved into the 

 depths of the cervical sinus. 



Fig. 287. -Longitudinal section through three olfactory buds from 

 the regio olfactoria of Belone, after Hi \ r : . llu'lily m.iunined. 



/*, Olfactory bn.l : ut ciliate e|itlifliuin in several 



layers; n, hianch <>f the olfactory nerve. 



gans (fig. 287 rk), which, although cK--ly < r>u<l <1 in an inditl- 

 ciliate epithelium (fe), are nevertheless srp.-. rat<<! iVnn each other. 



