438 



EMBRYOLOGY. 



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

 laginous base of 



the skull (schb) is 

 established, the 

 sac of the hypo- 

 physis (hy) comes 

 to lie above the 



latter at the under 

 surface of the be- 

 tween-brain (tr). 

 At this time also 

 the duct of the 



schb hyg sckb 



Fig. 248. Sagittal section through the hypophysis of a Rabbit 



embryo 20 mm. long, after MIHALKOVICS. Magnified 55 



diameters. 

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



hy 1 , 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. 



which meanwhile 

 has lost its lumen, 

 begins to shrivel 

 and degenerate 

 (tig! 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 



~ ch 



schb 



Fig. 249. Sagittal section through the hypophysis of a Rabbit 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 1 , the glandular tubules which have 

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

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

 em, epithelium of oral cavity. 



from the sella 

 turcica to the 

 base of the skull and receives a prolongation of the hypophysis 



(SUCHANNEK). 



