542 P. H. EDGEWORTH. 



The anterior or mandibular mylohyoid of Sauropsida pre- 

 serves the form existing in Scyllium — a transverse sheet of 

 muscle passing from one Meckel's cartilage to the other 

 (text-figs. 15 and 28, pp. 522, 531). 



The posterior or hyoid mylohyoid in iScyllium forms a 

 transverse band passing from one ceratohyal to the other. 

 The primary attachment of the muscle in Sauropsida is also 

 to the ceratohyal, but this is lost in all gi'oups with the possible 

 exception of Sphenodon.^ It gains, in all Sauropsida, a 

 secondary attachment to the lower jaw, becoming more or 

 less continuous with the anterior mylohyoid, and spreads 

 down the neck forming the constrictor colli. This posterior 

 part, which is attached laterally to the fasciae of the neck (in 

 Chelonia also to the first branchial bar, in Rhiptoglossa also 

 to the crista occipitalis) is continuous with the anterior part. 



In Gallus secondary changes take place in the posterior 

 mylohyoid. After a transitory stage of attachment to the 

 ceratohyal (text-fig. 12, p. 519) it becomes attached laterally 

 to the hind end of the lower jaw (text-fig. 13, p. 520) and first 

 branchial bar, and spreads down the neck. The portion 

 attached to the first branchial bar becomes a separate muscle 

 — th.e anterior constrictor colli^ — forming a muscular sling for 

 the second basibranchial (text-fig. 17, p. 524), whilst that in 

 front forms the serpihyoid and stylohyoid, that behind the 

 constrictor colli. The part attached to the lower jaw in the 

 Lamellicostren, however, forms a simple transverse band 

 (Gadow). The diiferentiation of an anterior constrictor colli 

 is evidently related to the existence of a second basibranchial — 

 it is absent in Keptiles, and in those Birds, e.g. Khea (Gadow), 

 where a second basibranchial is absent, and even when this 

 is present is not always developed. 



Laryngeal and Syringeal Muscles. — The Anlago of 

 the laryngeal muscles in Gallus is developed in the splanch- 



^ It was present up to stage S (of Howes and ISwiniierton), but is not 

 mentioned by Osawa. 



^ The " ceratohyoid " oi; Gadow, who incduded it aniony tlie lingual 

 muscles as a differentiated part of the ceratoglossus. 



