550 P. H. EDGEWORTH. 



that in the former the greater portion of the pterygoid 

 process disappears, the quadrate becoming secondarily mov- 

 able, the continuity of the ceratohyal is lost, and the bran- 

 chio-hyoid muscle also extends forwards to the lower jaw. 

 Further, whereas in the Rhyncocephalia the upper portion 

 of the mandibular myotome is inserted into the pterygoid 

 process with a very few fibres to the (fixed) pterygoid bone, 

 in the Lacertilia it is inserted into the (movable) pterygoid 

 bone, with a few fibres in some Lizards to the quadrate. 



The Ehiptoglossa and Ophidia present the Lacertilian 

 features of a movable pterygoid bone into Avhich is inserted 

 the upper part of the mandibular myotome and (in embryonic 

 stages) lingual muscles ending free in the tongue. Though 

 they differ markedly from one another in the adult form of 

 the tongue and in the associated condition of the hyobran- 

 chial visceral cartilages and lingual muscles, yet they possess 

 in common the following features which are not found in any 

 other groups — the non-development of a depressor palpebr^ 

 inferioris, an undivided pterygoid muscle arising from the 

 pterygoid bone, the partial origin of the depressor mandibulae 

 from the quadrate, and the secondary position of the cerato- 

 hyal internal to the quadrate. 



In conclusion, I have the pleasure of thanking Prof. W. N. 

 Parker for the loan of embryos of Chelone viridis. Prof. 

 F. S. Clarke for sections of Alligator mississipensis. 

 Prof. Moore for an embryo of Sphenodon, Mrs. Howes for 

 sections of Sphenodon, and Prof. Broom for embryos of 

 Agama and Chamaeleon. My thanks are also due to my 

 colleagues. Profs. Fawcett and Kent, for innumerable kind- 

 nesses. 



References. 



Bbadley. — "The Muscles of Mastication and the Movements of the Skull 

 in Lacertilia," ' Zool. Jahrb., Anat. und Ontog.,' Bd. xviii, 1903. 



BsooM. — "On the Development of the Pterygo-quadrate Arch in the 

 Lacertilia," ' Journ. of Anat. and Ph3's.,' vol. xxxvii, 1903. 



CoENlNG. — " Ueber die Entwicklung der Kopf- und Extremiliiten-niusku- 

 latur bei Keptilien," 'Morph. Jahrb.,' 1900. 



