HEAD-MUSCLES IN GALLUS AND OTHER SAUROPSIDA. 517 



embryo I had was too far advanced in development (chondri- 

 fication was complete) for one to see this stage — of a cerato- 

 liyal continuous from the hyomandibular above to the basi- 

 hyobranchial below. 



A first branchial bar is present in all groups of the Saurop- 

 sida^ a second branchial in Chelonia^ (vide text-tig. 19^ p. 525)^ 

 Sphenodon, and Lacertilia vera, but is absent in Birds, Croco- 

 dilia, Rhiptoglossa, and Ophidia. 



The main differences, consequently, between Birds and 



gef^ Q »"' 



2 tr my 

 l.trmy: 3trmy 



ant card v 



ant card I 



sup 



las 2gs. ^ 



Text-fig. 9. — Sagittal section through an embryo of Gallus, with 

 4 gill-pouches. It shows (partially) the formation of the ventral 

 longitudinal muscles, which originate from the first (half) myo- 

 tome and the four succeeding ones. Owing to the spiral twist of 

 the embryo no single section shows all the five downgrowths. (For 

 explanation of lettering see p. 555.) 



Reptiles in the state of the hyobranchial skeleton, are that in 

 the former a second basibranchial is developed ^ and the 

 median cartilages become jointed. There are correlated 



' The suggestions of Gaupp in regard to the nature of the cart, entoglossa 

 in Birds and the existence of a second branchial bar in Chelone are thus 

 confirmed. 



- It is absent in some few Birds, e. g. Rhea, Platalea. 



