ADAMS, PHYLOGENY OF THE JAW MUSCLES 65 



der Augenhbhle unterhalb des Processus praeorbitalis." Tiesing (Idem., 

 p. 86) classes this muscle with the dorsal constrictors: "Mit der Erkennt- 

 nis dass es sich um die Versorgung durch den Eamus III trigemni 

 handelt, verliert auch der M. Levator labii superioris die ihm von 

 friiheren Autoren zuerkannte selbstandigkeit und reiht sich dem system 

 der levators resp. dorsalen Constrictors im Trigeminusgebiet an." 



Levator maxillce superioris (L. m. s.). — This is one of the dorsal con- 

 strictors which arises on the skull, just anterior to the constrictor super- 

 ficialis dorsalis 1 (C^sd). It is inserted on the dorsal surface of the 

 palato-quadrate bar. This muscle is so closely associated with C^d in 

 both origin and insertion that most writers have placed them together. 

 Vetter (1874) places it with the dorsal constrictors and Marion (1905) 

 follows his determination. Vetter (1874, p. 408) gives the function of 

 the two muscles as follows: "Der Levator maxillae superioris und C^sd 

 heben den Oberkiefer, der erstere dreht ihn dabei um sein Gelenk mit 

 dem Schadel nach vorn, der letzere nach hinten." 



Constrictor (1) superficialis dorsalis (CjSd). — This small muscle is 

 just posterior to the levator maxillae superioris and is closely associated 

 with it. Both muscles represent a division of one of the dorsal series as 

 mentioned in the discussion of the other muscles. Its origin is on the 

 wall of the skull above the spiracle, from where it curves around the 

 anterior border of the spiracle to the insertion on the palato-quadrate 

 bar, just posterior to the insertion of the levator maxillae superioris. This 

 constrictor represents the dorsal part of the original dorsal constrictor 

 (CiSd) and in some pre-elasmobranch stage was probably much larger. 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY VII) 



There is no true depressor attached to the mandible in the elasmo- 

 branchs that has any connection with the dorsal part of the skull. The 

 depressing is performed by the long muscles of the hyoid region, assisted 

 by the coraco-mandibularis and coraco-hyoideus. These are hyoid arch 

 muscles and both are innervated by nerve VII as would be expected, as 

 they belong to the region of the second superficial constrictor. 



Constrictor (2) superficialis dorsalis (C 2 sd). — This is the large, undif- 

 ferentiated constrictor that in the higher forms is to become the depressor 

 mandibulae of the Amphibia, birds and reptiles ; but in the Pisces it is a 

 wide muscle arising from the posterior part of the skull and from the 

 fascia of the back muscles. It is inserted in the quadrate region of the 

 upper jaw onto the cerato-hyal cartilage and onto the tendinous bridge 

 of the dorsal and ventral constrictors. 



