438 



EMBHYOLOaY. 



takes place in tte connective tissue, by means of which the carti- 

 laginous hase of 

 the skull {schh) is 

 established, the 

 sac of the hypo- 

 physis (Jiy) comes 

 to lie above the 

 latter at the under 

 surface of the be- 

 tween-brain {tr). 

 At this time also 

 the duct of the 

 hypophysis {hyg), 

 which meanwhile 

 has lost its lumen, 

 begins to shrivel 

 and degenerate 

 (fig. 249). In 

 many Vertebrates, 

 however, as in the 



Selachians, it is retained throughout life and forms a hollow canal, 



which perfo- 

 rates the carti- 

 laginous base 



of the skull and 



is united with 



the epithelium 



of the mucous 



membrane of 



the mouth. In 



extremely rare 



cases there is 



retained in 



Man also a 



canal in the 



basi-sphenoid, 



which leads 



from the sella 



turcica to the 



sckb hyg schb 



Pig. 248, — Sagittal section through the hypophysis of a Kahbit 



emhryo 20 nun. long, after MihaIjKOVics. Magnified 55 



diametei's. 

 ir, Floor of the tetween-brain with infundibulum ; hy, hypophysis ; 



Ay*, part of the hypophysis in which the formation of the 



glandular tubules begins; hyg, duct of the hypophysis; 



schb, base of the skull ; ch, chorda ; si, dorsum sellse. 



schb 



Fig. 249. — Sagittal section through the hypophysis of a Babbit embryo 

 30 mm. long, after Mihalkovics. Magnified 40 diameters. 



tr, Floor of the between-brain with infundibulum ; hy, original pouch- 

 like part of the hypophysis ; hy*, the glandular tubules which have 

 budded out from the sac of the hypophysis; si, dorsum sellse; 

 ba, basilar artery; ch, chorda ; scib, cartilaginous base of the skull; 

 em, epithelium of oral cavity. 



base of the skull and receives a prolongation of the hypophysis 

 (StjchannEk). 



