HEAD-MUSOLES IN GALLUS AND OTHER SAUROPSIDA. 543 



nic mesoblast of tlie second brancliial segment on the 

 sixtli day. A day later each lateral mass has divided into 

 an apertor and its lateral half of the sphincter laryngis. 

 The laryngeal muscles of Sphenodon, Agama^ Chelone, 



ffass.p. 



mend^ my.o p 



R Sup 



ply pr of quad. pal pter bar pty 



Me. ' gen.hyoid 



ant my Jo. post myio. 



Text-figs. 37 and 38. — Sagittal sections througli an older embryo 

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



Alligator, Chamaeleon, and Tropidonotus are formed simi- 

 larly from an Anlage in the second branchial segment. 



The syringeal muscles of Gallus are formed from meso- 

 blast cells which have spread down the trachea, and their 

 Anlage is visible on the eighth day. 



VOL. 51, PART 4. NEW SERIES. 41 



