438 



EMBRYOLOGY. 



schb hyg schb 



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 ; liy, hypophysis ; 



litf, part of the hypophysis ia which the formation of the 



glandular -tubules begins ; hyg, duct of the hypophysis ; 



schb, base of the skull ; ch, chorda; al, dorsum sells. 



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 

 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 hy 



membrane of 



the mouth. In 



extremely rare scltb 



cases there is 



retained in 



Man also a em 



canal in the 



basi-sphe n o i d, 



which leads 



from the sella 



turcica to the 



base of the skull and receives a prolongation of the hypophysis 



(SUCHANNEK). 



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 ; liij ', the glandular tubules which have 

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

 6a, basilar artery; ch, chorda ; sM, cartilaginous base of the skull; 

 em, epithelium of oral cavity. 



