HEAD-MUSCLES IN GALLUS AND OTHER SAUROPSIDA. 547 



longitudiual muscles; it would seem probable that their 

 original function was to connect the basihyobranchial with 

 the lower jaw and first branchial bar, and that their extension 

 into a tongue was a secondary matter. Only by this suppo- 

 sition do the phenomena occurring in Chelone, Alligator, 

 Sphenodon, Gallus, and Procellaria become explicable. 



Some Theoretical Conclusions. 



The above observations suggest that some remote ancestor 

 of the Sauropsida possessed, the fellowing features : — A mov- 

 able pterygo-quadrate, fixed palate and pterygoid bones, a 

 ceratohyal which formed a continuous bar extending from 

 the hyomandibular above to a median unjointed basihyo- 

 branchial below, first and second branchial bars. The eye- 

 muscles consisted of four recti, two obliqui, and the retractor 

 oculi. The mandibular myotome had divided into an upper 

 and a lower part ; the upper formed the depressor palpebrae 

 inferioris and an elevator of the pterygoid process of the 

 quadrate ; the lower consisted of an inner and an outer divi- 

 sion, the inner forming the pterygoid muscle which arose by 

 two heads — from the pterygoid bone and from the pterygoid 

 process of the quadrate, the outer forming the temporal 

 muscle, which arose partly from the quadrate and partly from 

 the skull wall above. The hyoid myotome formed the 

 depressor mandibulse. The first branchial myotome formed 

 the branchiohyoid muscle passing from the first branchial 

 bar to the ceratohyal. The ventral longitudinal muscles 

 were formed by a genio-hyoid and a sterno-hyoid, whose 

 adjacent ends were attached to the first branchial bar. The 

 lingual muscles — developed from the genio-hyoid — were the 

 genio-glossus and the hyo-glossus, the former passed from the 

 anterior end of the lower jaw to the anterior end of the basi- 

 hyobranchial, the latter from the first branchial bar to the 

 side of the basihyobranchial ; neither ended free in the tongue. 

 The anterior and posterior mylohyoids formed a continuous 

 sheet and extended down the neck. 



