THE MUSCLES 57 



Occipito-mandibularis s. Digastricus . . . Owen (1866). 



Digastric Mivart (1869). 



Digastric et Depressor mandibulae , . , Humphry (1872). 



Cephalo-dorso-maxillaris s. Digastricus-maxillae Hoffmann (1873-8). 



Camd Ruge (1897). 



Cephalo-dorso-mandibularis ..... Driiner (1901). 

 A thick, powerful muscle originating from the posterior edge of 

 the squamosal, the 'crista muscularis' of the ear capsule, and 

 the anterior portion of the fascia cephalodorsalis (Driiner). This 

 superficial dorsal fascia gives origin to a number of muscles. It 

 is firmly united to the skin and extends backwards to behind the 

 shoulder. Edgeworth (i 93 1) has shown that the M. depressor man- 

 dibulae is derived from the M. levator hyoidei of the Dipnoi. 



Innervation: From R. jugularis VII by a fine branch which separ- 

 ates from the main nerve immediately distal to the point at which the 

 R. communicans IX+X ad VII is received. It enters the muscle 

 mesially. 



Function: As its name implies, it is the opening muscle of the lower 

 jaw and opposes the levator mandibulae. 



The M. interhyoideus (PI. VI, fig. 37) is the next muscle to be 

 considered. It undergoes a rather considerable change during meta- 

 morphosis, and becomes divided into two portions. The anterior 

 portion retains more or less the original position and therefore 

 retains also the original name — M. interhyoideus, while the posterior 

 portion shifts backwards and hence becomes the M. interhyoideus 

 posterior. Most of the earlier authors regarded the whole muscle as 

 the posterior part of the 'Mylohyoideus'. Both portions together are 

 spoken of as 'Duo-cutis musculi oriuntur in maxillae inferioris unco' 

 by Carus (1828). 

 M. interhyoideus (Edgeworth) (m.i.hy.). 



Constrictor pharyngis internus . . . v. Siebold (1828). 



Mylohyoidien, portion moyenne .... Rusconi (1854). 



Cghv Ruge (1897). 



Inter-ossa-quadrata ...... Driiner (1901). 



The origin of this muscle is by means of a short thin tendon from 

 the postero-mesial edge of the quadrate, just ventral to the point 

 of insertion of the ligamentum hyoquadratum. According to Driiner 

 some fibres may occasionally arise from the ligament itself. The 

 fibres spread out fan-wise over the hinder part of the mouth-floor, 

 and are inserted into a posterior continuation of the median apo- 

 neurosis of the M. intermandibularis posterior. The direction of the 

 most posterior fibres is thus almost directly transverse and that of 



