HEAD-MUSOLES IN GALLUS AND OTHER SAUROPSIDA. 515 



subsequently stated that in a five-day-old chick each cerato- 

 hyal is continuous below with a " branchial blastema." 



Transverse sections show that whereas the lower ends of 



pretnand segsn 



Text-fig. 6. — Transverse section through an embryo of Gallus, 

 showing fully formed Anlage of premandibular segment. (For 

 explanation of lettering see p. 555.) 



the first branchial bars meet each other in the middle line, the 

 lower ends of the ceratohyals are separated from one another 



ven cepfi ccel ■ 



Text-fig. 7. — Transverse section through an embryo of Gallus, 

 with 3 fully formed gill-pouches, in hyoid and first branchial seg- 

 ments. (For explanation of lettering see p. 555.) 



by a median procartilaginous structure (text-fig. 12, p. 519), 

 which is continuous with a median structure in front and 

 behind. Chondrification takes place, the middle portion of 



