438 



EMBRYOLOGY. 



_ tr 



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) t 

 which meanwhile 

 has lost its lumen, 

 begins to shrivel 

 and degenerate 

 (fig. 249). In 

 many Vertebrates, 

 however, as in the 



schb 



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 inf undibulum ; hy, hypophysis ; 

 htf t 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. 



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 



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', the glandular tubules which hav 

 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. 



base of the skull and receives a prolongation of the hypophysis 

 (SUCHANNEK). 



