THK OUGAXS OF TIIK otTKK <JKK.M-l.AYKi:. 



437 



has jusr arisrii and is still separated from tin- cavity .f l ho head-gut 

 t.y meutfl ol tin' pharyngeal membrane (rA). At this time the 

 cephalic tlexure of the 1 -rain- \ esides has already appeared, and the 

 i'-r end of the chorda dorsalis (ch) terminates immediately 

 behind (In- attachment of the pharyngeal membrane. In fn>i 

 this i^ heated ihe important pi a c \v I IM t he hypophysis is developed, 

 as was first established by GOKTTK and M in M.KOVICS. The I 

 y/////s/s /s //,, re fore a pr< '<e outer y and not a growth 



from (lie cavity of the head gut, as had always been maintained 

 pre\ inn- to tlii- time. 



The first steps introductory to the formation of tin- hypophysis 

 tab place soon after the rupture of the pharyngeal membrane 

 (figs. 238, 247), some unimportant remnants of which are retained 

 at the base of the skull as the so-called priin num. 



Anterior to these there is now developed (in th<> Chick on the 

 fourth day of incubation, in Man during tin- fourth \vr-k. Hi- 

 small c\ agination, the pouch O/*RATHKE or the kyns 



(/<//) which grows to- 

 ward the base of the 

 b e t w e e n-b rain (tr). 

 Tli* MI it becomes deeper, 

 1't'^ins t> be constricted 

 off from its parent tissue, 

 and to be metamor- 

 phost d into a small sac, 

 \\hos- wall is compo-rd 

 of several layers of c\ 1 i n - 

 drical cells (fig. 248). 



TJie sac of the hypo- 

 physis (hy) remains for 

 a long time in connec- 

 tion with the oral ca\ it y 

 by means of a narrow 

 duct (hyy). In later 

 Ma gos, however, the 

 connection in tho 

 higher Vertebrates is 



interrupted, because the embryonic comuvtiv tissue, \\hich supplies 

 the foundation for the development of the skeleton of the head, 

 becomes thickened and crowds the sac farther away from the oral 

 cavity (figs. 248, 249). When, later on, the process of chondrification 



Fig. 247.- Median sagittal section through the hypophysis 

 of a Kabbit embryo 12 mm. long, a: .vies. 



Magnified 50 diameters. 



>r of the between-brain with the infundibulum ; 

 nh, floor of the after-braio ; ch, chorda ; Ay, pocket 

 of the hypophysis. 



