ADAMS. rHYLOGEXY OF THE JAW MUSCLES 69 



MUSCLES or THE ADDUCTOH oh 'lEMl'Oh'AL GROUP 

 (IXXEh'VArEI) JiY Tj) 



Adductor mandihuhc (Ad. m.). — This is a small muscle that arises 

 on the upper side of the palato-quadrate region. It curves around and 

 is inserted on the small Meckelian cartilage. It raises the mandible and 

 presses it against the marginal cartilages of the maxillary region. 



Protractor hyomandihularis (P. h.). — This is a large muscle in the 

 sturgeon. It arises in the post-orbital region, extends ventro-posteriorly 

 and is inserted on the hyomandibular. It is concerned in the action of 

 the gill apparatus and in the sucking action, 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 tlXXERVATED BY ] II) 



Retractor tnjoinandUnilaris (R. h.). — It arises on the skull wall back of 

 the spiracle and is inserted on the dorsal edge of the hyomandilndar. It 

 raises the gill apparatus. 



Levator operculi (L. o.) (Abetter, 1874). — This arises along the side 

 of the skull, just posterior to the origin of the retractor hyomandihularis. 

 It is inserted on the operculum on the inner side. It pulls up the oper- 

 culum. 



A3HIA 

 Plate II. Figs. 1. 2 



In the very ]irimitive skull of Anna, the chondrocranium is hut little 

 ossified and the dermal plates are still on the surface and ver\' much of 

 the primitive ganoid pattern. The hyomandibular and preopercular are 

 sunken deeper into the skin, so tliat the adductor is of the teleost type, 

 with its origin on the anterior face of the preopercular. The cartilagi- 

 nous palato-quadrate and the ]\reckelian cartilage are incased in their 

 dermal bones, and good teetli have developed, so there is need of good 

 muscular development for the jaws. The quadrate, preoperculnm and 

 the cartilaginous skull make a good insertion for the splendid muscular 

 system found in this group. The insinking of the preopercnlum gives 

 the adductor plenty of room for development and full advantage has 

 been taken of this opportunity.^ 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GHOVP 

 (INNERVATED liY V^) 



Levator maxilUr superioris (I^. m. s.). 



''This study on Amia follows the work of Allis (1S0T» :in<l McMnrrich (1885K 



