ANATOMY OF A 17.8 MM. HUMAN EMBRYO 69 



just dorsal to the ampulla of the lateral semicircular canal. 

 This diverticulum joins the crus commune of the superior and 

 posterior semicircular canals without, however, opening into it. 

 This diverticulum, does not occur upon the left side, but a simi- 

 lar condition in other human embryos of the Harvard Collection, 

 has been observed by the author. 



Nose 



The nares are represented in plates 3 and 5, and the ectodermal 

 linirg of the olfactory vesicles in plates 1, 2 and 4. 



The nares (Na.) are open, but separated by a broad septum, 

 From the naris each olfactory pit (Ves.olf.) extends dorso-cau- 

 dally as a small tube, oval in transverse section. Each tube 

 shortly expands to form the main nasal cavity which opens into 

 the fore part of the roof of the mouth by a large primitive choana 

 {Ch.pr.). 



In lateral view (plate 2) the epithelial wall of the olfactory 

 vesicle presents cephalad a large concavity partially subdivided 

 by a slight external ridge (unfortunately not shown in the draw- 

 ing) into a shallow dorsal depression, the nasoturbinal (agger 

 fiasi), and a more extensive ventral one (Max-turb.), the maxillo- 

 turbinal (concha inferior). The maxilloturbinal is limited ven- 

 trally by a pronounced, somewhat dorsally curled fold of the 

 vesicular wall, containing within the meatus nasi inferior. 



At the dorsal part of the choanal extremity of the olfactory 

 vesicle there is seen in a lateral view a slight indentation {Eth.- 

 iurh.I), representing the developing ethmoturbinal I (concha 

 media). The ethmoturbinal I, although it now forms in part the 

 lateral wall of the olfactory vesicle, has been shown by Peter ('01) 

 to be a derivative of the septal wall. The ridge appearing be- 

 tween the ethmo- and maxillo-turbinal overlies the meatus nasi 

 medius. The palatal process forms the lateral boundary of the 

 choanal extremity of the olfactory vesicle. 



On the medial wall of the olfactory vesicle (plates 1 and 4) 

 is seen the small, tubular outgrowth (Org.vom.-nas.) for the 

 vomero-nasal organ (Jacobson's), rudimentary in man. 



