582 ALLIS. (VoL. XII. 
importance, for the nerve seems to lie always between A; and 
Az, a position derived directly from that found in selachians. 
Apparent departures from this position are often given, but in 
the three cases that I have examined, namely, Esox, Amiurus, 
and Moxostoma, it seems due to a misconception of the dif. 
ferent parts or layers of the muscle, and not to a variation 
in the position of the nerve. In Esox no part of the muscle 
Az of Vetter is inserted on the hind edge or outer surface of 
the mandible, the entire muscle joining, or passing into, the 
well-developed mandibular muscle do, and having its insertion 
with that muscle inside the ramus of the mandible. A super- 
ficial portion is, however, indicated, and it is along and slightly 
under the front edge of this portion, between it and the bundle 
A38, and then on the outer surface of Aa, that the inferior 
maxillary nerve enters the mandible. Vetter’s description, 
which leads one to infer that the nerve enters the mandible 
between Az and A3, that is, internal to the tendon Az Aa, 
which it must therefore first pierce to reach its later position 
on the outer surface of Aw (No. 125, p. 495), is anerror. In 
Amiurus some of the superficial fibres of Az, the AM of 
McMurrich, are inserted on the hind edge of the mandible, 
and as the inferior maxillary nerve enters the mandible along 
their front edge, on the outer surface of the remaining, deeper 
portion of the muscle, these fibres undoubtedly represent Ar. 
In Moxostoma, where A; is found well developed, the inferior 
maxillary nerve lies along the front or upper edge of Az and 
not internal to it, that is, between it and A3, as Vetter 
describes it in Cyprinus and Barbus. 
d. Intermandibularis, Geniohyoideus, and Hyohyoideus. 
These three muscles are derived by Vetter from the ventral 
portion of that part of the general constrictor that, in selachians, 
lies in front of the first gill slit. In the earlier part of his 
work Vetter states (No. 124, pp. 411, 417, and 426) that this 
part of the constrictor is innervated by the facial alone, and 
that it accordingly belongs entirely to the hyoid arch. Tiesing’s 
results agree with this earlier work of Vetter’s. Vetter, how- 
