540 r. H. EDGE WORTH. 



ceratoliyal, for it occurs in Cliam?eleon before tliis takes place. 

 Probably it is related to the extension backwards of the jaw 

 into the hyoid segment. In Chelonia the anterior attachment 

 of the branchio-maxillaris muscle is to the hind eud of the 

 lower jaw, in the other groups the muscle extends still further 

 forwards — in Rhiptoglossa even as far as the symphysis. 



The branchio-hyoid or branchio-maxillaris muscle of 

 Sauropsida is homologous Avitli the most anterior of the 

 coraco-branchiales muscles of Scyllium. 



Myotome of the Second Branchial Segment. — A 

 myotome is developed in the second branchial segment in 

 Gallus (text-fig. 4, p. 514), but disappears leaving no trace. 

 In Lacerta, too, a second branchial myotome is described by 

 Corning, but there are no muscles present in the embryos of 

 Agama investigated or in adult Lacertilia which might have 

 developed from the myotome. And in the other Reptilian 

 embryos the stages were likewise too far advanced for any 

 rudiments of this myotome to be seen. In the Sauropsida, 

 then, a second branchial myotome, if formed, soon disappears 

 and does not develop into any muscle. 



Its existence, however, though only as a temporary structure 

 in Gallus and Lacerta, coupled with that of a second branchial 

 bar in Chelonia, Rhyncocephalia, and Lacertilia vera, sug- 

 gests that ancestors of Sauropsida may have possessed a 

 longitudinal muscle connecting the secoud to the first 

 branchial bar. 



Cephalic Section of the Coelom and Mylohyoid 

 Muscles. — There are certain similarities and differences 

 between Scyllium and Gallus in the relations of the ventral 

 cephalic coelom to the heart and visceral muscles of the mandi- 

 bular and hyoid segments. In early stages of Scyllium there 

 is, in the mandibular and succeeding segments of the head, 

 a ventral section of the cocloui which bears the same relation 

 to the ventral aorta as does the anterior portion of the body 

 section of the coelom to the truncus arteriosus and the heart. 

 Subsequently, the developing heJirt bulges into the hinder 

 portion of the cephalic coelom. Still later, the heart and 



