ADAMS, PHYLOGENY OF THE JAW MUSCLES 67 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 (INNERVATED BY V z ) 



The adductor mandibular is divided into two parts: a large anterior 

 portion, and a smaller deep part. The large portion extends anteriorly 

 along the palato-quadrate bar, while the posterior, deep, portion is a short 

 muscle from the quadrate region. 



Adductor mandibulce 1 (M. adm. of Danforth). — This is the larger 

 section of the adductor which lies over the palato-quadrate bar, curves 

 around the quadrate and is inserted in the suprameckelian fossa. Its 

 origin starts on the dorsal, anterior end of the palato-quadrate and ex- 

 tends backward, overlapped slightly along its ventral side by the maxilla ; 

 it curves downward under the maxilla at a sharp angle and is inserted 

 into the suprameckelian fossa and also on the dentary. Its curve is very 

 abrupt, so that its insertion is at right angles to the main mass of the 

 muscle. 



Adductor mandibulce 2 (M. adm. 1 of Danforth). — Just posterior to 

 the abrupt curve of the adductor mandibular 1 arises the adductor man- 

 dibular 2 on the posterior end of the palato-quadrate bar. It extends 

 ventrally to be inserted on the dentary and in the suprameckelian fossa. 



Danforth (1913, p. 116) mentions some speculations in regard to the 

 adductor mandibular 1 of Polyodon that are rather interesting and per- 

 fectly justified from the conditions. He 



In Acipenser there is, in addition to the adductor mandibular, a strong con- 

 strictor (Cs of Vetter) which overlies it. The latter arises from the antorbital 

 process and extends around the lower jaw. The anterior part of the adductor 

 in Poly don has a superficial resemblance to this muscle, but none of its fibers 

 arise from any part of the cranium proper and I have been unable to find any 

 indication that they ever pass over into the ventral constrictor, below the jaw. 

 Consequently from the adult material alone, it cannot be stated with any cer- 

 tainty that the anterior adductor of Poly don finds its homologue in the con- 

 strictor of Acipenser, although there is a possibility that such is the case. 



From its position, it could be a part of the constrictor superficialis 1 

 of Vetter, as Danforth suggests. It is tempting to imagine that the old 

 origin on the skull has been lost and that it slipped down to its present 

 position. Several other forms have a muscle of this type and the embry- 

 ology should show the truth or falsity of the assumption. This muscle 

 protracts and closes the mouth. 



Protractor hyomandibularis (P. hy.). — This muscle strongly suggests 

 the similar muscle in Acipenser. It is a double-headed muscle that 

 arises from the base of the skull at the posterior end of the roof of the 

 mouth and from the post-orbital process, anterior to the spiracle. It 



