58 THE SALAMANDER 



the anterior ones obliquely antero-mesial. The mesial ends of the 

 anterior fibres lie dorsal to the M. intermandibularis posterior. 



While this portion of the muscle retains its original position, its 

 origin has nevertheless shifted, and has migrated from the posterior 

 end of the hyoid arch, passing up the lig. hyoquadratum to the 

 quadrate. 



Innervation'. By the terminal branches of R. jugularis VII which 

 spread over its ventral side. 



Function'. It constricts the hyobranchial skeleton and posterior 

 part of the mouth, and thus assists both in respiration and deglu- 

 tition. 



M. interhyoideus -posterior (Edgeworth) (m.i.hy.p.). 



Constrictor pharyngis externus 

 Mylo-hyoidien, partie posterieure 

 Mylosternoideus 



V. Siebold (1828). 

 . Rusconi (1854) 

 . Walter (1887}. 

 Ruge(i897). 

 Quadrato-pectoralis ...... Driiner (1901). 



The posterior portion of the interhyoid muscle arises by means of 

 a strong tendon from the ventro-lateral surface of the quadrate and 

 the distal end of the squamosal. Its fibres spread out fan-wise across 

 the throat ventral to those of the preceding muscle. The muscle 

 becomes joined to the capsule surrounding the articulation of the 

 jaw as it passes laterally across it. The direction of the anterior fibres 

 is almost transverse, and they are inserted in backward continuation 

 of the same aponeurosis as receives the MM. intermandibularis and 

 interhyoideus. The most posterior fibres, forming the bulk of the 

 muscle, turn more postero-mesially and are inserted into the skin at 

 the gular fold. This fold of skin surrounds the throat on the ventral 

 side, and represents the remains of the gill operculum of the larva 

 fused with the skin of the pectoral region. To the same fold, posteriorly, 

 is attached the base of a triangular aponeurosis — th.e. fascia pectoralis 

 (Driiner) — the apex of which is directed backwards and is attached 

 to the most anterior fibres of the M. pectoralis, so that by this means 

 the two muscles, the M. interhyoideus posterior and the M. pecto- 

 ralis are to some extent associated. The M. interhyoideus posterior 

 lies ventral to the MM. procoraco-humeralis and supracoracoideus, 

 which arise from the pectoral girdle, and is loosely attached to them 

 by connective tissue. 



This muscle is peculiarly an adult structure, and Druner was 

 somewhat doubtful as to its derivation, but thought that it might 

 have arisen from the M. interbranchialis i. Edgeworth, however. 



