ADAMS, PHYLOGENY OF THE JAW MUSCLES 73 



the operculum, near its anterior edge. It pulls the operculum forward 

 .and is homologous with the muscle of the same name in Amia. 



Levator operculi (L. 0.). — This arises on the occipital region of the 

 skull, spreads out in a fan-like insertion on the upper, inner face of the 

 operculum. It raises the operculum. Both of these muscles are prob- 

 ably the homologues of Csd 2 of Vetter and the C 2 md of Euge. 



ESOX 

 Plate III, Figs. 1, 2 



In Esox, as in other teleosts, the dermal bones have sunk into the 

 skin so that the adductor region is free on the outside. The preoper- 

 culum, metapterygoid, quadrate, and post-frontal regions give the ad- 

 ductors a good surface for insertion. The teleost mandible becomes en- 

 larged and the articulation with the quadrate is greatly improved in its 

 mechanics. As the maxillae are reduced and have lost the power to meet 

 the mandibles, their teeth have disappeared and the mandibles are in- 

 clined inwards to meet the teeth of the palatines. 



The following description is based partly on that by Vetter (1878) : 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 (INNERVATED BY F 3 ) 



Adductor mandibular 4 (Add. <» of Vetter). 



Adductor mandibular 1 (Superficial). 



Adductor mandibular 2 + 3 (To symplectic, etc. Deep.). 



Levator arcus palatini (Vetter). 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY VII) 



Adductor hyomandibularis (Vetter). 

 Dilator operculi (Vetter). 

 Levator operculi (Vetter). 

 Adductor operculi (Vetter). 

 For homologies see Table I, p. 156. 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 (INNERVATED BY VJ 



The muscles of Esox have been worked out by Vetter (1878, p. 494). 

 His names are used for the most part in the present description, although 

 the nomenclature of the adductor mandibular is changed, as explained in 

 the notes. The adductor has three distinct parts. 



