574 ALLIS: [VoL. XII. 
inner strand of the nerve, corresponds to the fourth division. 
This nerve was traced in Galeus on one side only of a single 
specimen. Its being double suggests an explanation of an 
apparently abnormal innervation of Lms* by the superior max- 
illary nerve, found in one specimen of Amia. The strand 
destined for the innervation of this muscle in this particular 
specimen had doubtless become separated from the rest of the 
nerve and attached secondarily to the superior maxillary which 
it so closely accompanies. It arises in Galeus from the upper 
surface of the truncus trigeminus, while in Amia it arises from 
the under surface of that truncus, an important difference. 
In Galeus it partly encircles the inferior maxillary, holding that 
nerve as ina loop. If this position of the nerves represents 
an earlier condition than that found in Amia, the inferior maxil- 
lary, as it moved backward to the position found in Amia, must 
have caused an apparent shifting of the origin of the nerve 
from the upper to the under surface of the truncus. 
The innervation of the smaller spiracle muscle in Galeus was 
not determined. The muscle may, from its position, be de- 
rived either from Csd; or from Addy. The innervation of the 
spiracle muscles in Mustelus by two nerves suggests that they 
are of similar, but perhaps not of identical, origin. The same is 
true of the muscles innervated by the double nerve in Galeus. 
It therefore seems probable that Csdi1, Lms, AddB and Addy 
in Heptanchus, Carcharinus, and other selachians, represent 
parts of the constrictor superficialis dorsalis of the mandibular 
arch, or that they represent parts of that constrictor and parts 
also of the corresponding portion of the constrictor of one or 
more preoral arches. From Addy the levator arcus palatini 
and dilatator operculi of Amia are derived, and possibly also 
one of the spiracle muscles in Galeus and Mustelus ; from Csdr 
is derived the larger spiracle muscle of Galeus, or perhaps both 
the spiracle muscles; from the larger spiracle muscle of Galeus 
is derived the muscle Zs* of Amia; from the levator maxillae 
superioris of selachians is derived the muscle Zs? of Amia; and 
from Add (the levator labii superioris of Tiesing) the muscles 
Lms3 and Lms‘. In rays this last muscle splits up, according 
to Tiesing, into several more or less independent portions. 
