188 EMBRYOLOGY OF THE LOWER VERTEBRATES CH. 



cnt. 



b.d.1 



bd.2- 



td.2 



ent 



Ki-,. 10*. Illi; !y <l.-vrlii|uii.-iit <>l tin- 



livi-r in Minis. 



A, 47-lionr Hih-k : H. .V_- hour chirk : < '. .Mi-h our chick 

 (after Hr-.m. D I'.iiith-luy rln.-k ; K, 7 nun. 



mbry, of Din KoM-at.- I 

 Hamiu - '. iii'liiii.-nt ..! ani.-imi , 



ilnct ; ' \it\ ..i 



1 ; '/'-, niiliiiioit ul'^'ill-l. ni. -i n >r 



-I rii'liini-nt 

 of pancreas. 



portion of the rudiment. The 

 Lcall Madder originates as a 

 bulging of the floor of the 

 bile-duct towards its anterior 

 end. 



The formation of the pos- 

 terior and longer section of 

 the bile-duct, which will be 

 extrahepatic in the adult, 

 lags in its development behind 

 the anterior portions of the 

 rudiment. Such differences 

 in the time of appearance of 

 different parts of the hepatic 

 apparatus liver, gall-bladder, 

 bile-duct are to be looked on 

 as mere secondary modifica- 

 tions of development, the 

 primitive condition being that 

 of a simple pocket of the gut- 

 wall such as persists in Am- 

 pliioxus. 



SAUROPSIDA. The hepatic 

 apparatus here again makes 

 its appearance as a longi- 

 tudinally situated pocket of 

 the morphologically ventral 

 wall of the gut. In birds 

 this is situated at first on the 

 anterior wall of the yolk-stalk 

 (Fig. 108, A). The diverti- 

 culum grows actively into an 

 anterior (dorsal) and a pos- 

 terior (ventral) pocket (Fig. 

 108, C, li. 1 and li. 2) while 

 the intervening portion In- 

 comes flattened out and incor- 

 porated in the gut- wall. 



There thus come to be two 

 ilistinct liver -rudiments an 

 anterior and a posterior. Of 

 t.hrse each sprouts out at its 

 IK! into invii-nlar projcrt ions 

 \vliic.li r\vntually fuse and 

 form a sj.oimy mass, surnumd- 

 inu tli' cavity of tin- duct us 

 venosus. and having in it' s 

 MM' IH-S Mood-spares which 



