THE MYOLOGY OF AMIURUS CATUS. 313 



lum, and thence to the quadrate. Certain fibres also take origin 

 from the surface of the hyomandibular and from the transverse ridge 

 on that bone. These fibres are at first distinct from the main muscle 

 but soon unite with it. The lower fibres pass obliquely forward, and 

 are inserted directly into the posterior edge of the process of the 

 articulare, uniting partly with the remaining fibres. These converge 

 towards the inner surface of the mandible, uniting to form a tendon 

 on the inner surface of the muscle which is inserted into the longitu- 

 dinal ridge on inner surface of articulare and the inner surface of 

 the dentary, Meckel's cartilage receiving also some fibres. 



Innervation. — It is supplied by the trigeminus. The deeper 

 portions are supplied by a branch arising from the upper lateral 

 strand of the trigeminus before its division into the superior and in- 

 ferior maxillary branches. The superficial portions are innervated 

 by a branch arising just behind this. 



Action. — The add. mand, raises the jaw after it has been depressed 

 by the geniohyoid, and is therefore the opponent of that muscle. 



In most Teleostei the add. mand. consists of three portions, of 

 which the upper passes to the maxilla, the others to the mandible. In 

 Esox, an arrangement more related to that occurring in Amiurus ob- 

 tains. The superficial portion is wanting, but the other two portions 

 are distinct. Of these the upper, arising from the upper part of the 

 semicircular ridge and inserted into the inner surface of the articu- 

 lare and Meckel's cartilage, corresponds to the upper portions of the 

 muscle in Amiurus ; while the deeper one, arising from the mefcapt- 

 erygoid and lower part of the semicircular ridge and inserted into 

 Meckel's cartilage, a tendon uniting with that of the upper portion, 

 corresponds with the lower portion of the muscle in Amiurus plus 

 that arising from the transverse ridge and sui'face of the hyomandi- 

 bular which here usurps the position of the metapterygoid, the 

 slight difference in the insertion being no greater than that which 

 obtains fc Esox and Barbus in the deeper portions, which in these 

 forms are clearly homologous. From the position of the muscle one 

 may conclude that it is an angular structure, i.e., belonging equally 

 to the upper and lower moieties of the first post-oral arch, and this 

 conclusion is confirmed by the innervation, the supplying branches 

 leaving the trunk of the trigeminus before its division into the 

 superior and inferior maxillary branches. Since the maxilla is a 

 splint-bone belonging to the upper half of this arch, one would sup- 



