522 



F. H. EDGE WORTH. 



Muscles. 



The premandibulav segments are formed in Gall us by 

 hollow lateral outgrowths from the anterior end of the fore- 

 gut, which, a little later, is constricted off, forming a canal 

 connecting the vesicles (text-figs. 5 and 6, pp. 514, 515). The 

 lumen in the canal disappears, and the resultiug column of 

 cells atrophies. The vesicle, on either side, becomes a solid 



sphen p n gang ofVi 



mand. my u p 



pty pf of Qijsd 

 pal pter bar 



ont.my/o gen hyoid 



Text-fig. 15. — Transverse section througli an embryo of Gallus 

 at beginning of seventh day. (For explanation of lettering see 

 p. 655.) 



clump by proliferation of its lining cells, and develops into 

 the eye-rauscles innervated by the third nerve. 



In the Liza,rd' and Duck ^ the preraandibular segment is also 

 formed from the hypoblast, though in a slightly different way 

 — by solid lateral outgrowths from the dorsal wall of the 

 foregut, which are cut off, and develop a cavity extending 

 from side to side. In the Lizard the eye-muscles begin to 



' Corning (loc. cit.). 

 - Rex (loc. cit.). 



