HEAD-MUSCLES IN GALLUS AND OTHER SAUROPSIDA. 519 



stapedial portions, the extra- and supra-stapedial portions 

 lying internal to the quadrate. Study of the development, 

 however, shows that his " extrastapedial " is the persisting 

 upper end of the ceratohyal which lies at first posterior to the 

 quadrate (text-figs. 32 and 33, p. 536) in the hyoid segment. 

 A true extrastapedial is absent. 



The hyoid bar of Tropidonotus similarly lies at first in the 

 hyoid segment (text-fig. 37, p. 543). The '^ tuberculum " (of 

 Parker) attached to it is probably a suprastapedial element ; it 

 is developed as an outwards and upwards projecting process of 



ven car art 



-J 



J'ertv >^'- *^ S« 



Text-fig. 12. — Transverse section through an embryo of Gallus 

 at the beginning of the sixth day. (For explanation of lettering 

 see p. 555.) 



the hyoid bar (at a stage later than that shown in text-fig. 37, 

 p. 543), and only subsequently rotates forward. Parker stated 

 that the " tuberculum " became adherent to the stapedial j)late, 

 but so far as my observations go it simply disappears. The 

 " stylohyal," of Parker, which becomes adherent to the inner 

 face of the quadrate is the separated lower end of the hyoid 

 bar. 



In both Chamaeleon and Tropidonotus the hyoid bar thus 

 assumes a secondary position internal to the quadrate, 



