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THE MYOLOGY OF AMIURUS CATUS. ole 
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 geniohyo/d, 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 Amiwrus 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 Amiwrus ; while the deeper one, arising from the metapt- 
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 Amiwrus plus 
that arising from the transverse ridge and surface 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 in Hsox 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, 7.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- 
