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), 

 which meanwhile 

 has lost its lumen, 

 begins to shrivel 

 and degenerate 

 (fig. 249). In 

 many Vertebrates, 

 however, as in the 



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 inf undibulum ; hy, hypophysis ; 



hy", 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 

 retained 

 Man also 



IS 



iii 

 a 



canal in the 

 basi-sphenoid, 

 which leads 

 from the sella 

 turcica to the 

 base of the skull 



(SUCHANNEK). 



schb _ 



Fig. 249. Sagittal section through the hypophysis of a Rabbit embry* 

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



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

 like part of the hypophysis ; htf, the glandular tubules which have 

 budded out from the sac of the hypophysis; si, dorsum sell*; 

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

 em, epithelium of oral cavity. 



and receives a prolongation of the hypophysis 



