568 ALETS. [Vov. XII. 
are concerned. It seems, however, proper to attempt to bring 
my results into some sort of accord with, or relation to, those 
of others. In doing this, I shall frequently refer to dissections 
made of several fishes, more particularly of Carcharinus littor- 
alis and Galeus canis, in the earlier stages of this investigation. 
They were made most superficially, and simply to determine, 
approximately, certain points that I thought obscure but of 
importance in Vetter’s descriptions. Notes and sketches were 
made at the time, and, as I have only them to refer to, the 
statements now made regarding the several fishes may not be 
entirely reliable. 
a. Levator Arcus Palatini, Dilatator Operculi, and Muscle 
Addy. 
The levator arcus palatini and dilatator operculi are certainly 
parts of a single muscle. They are considered by Vetter (No. 
125, pp. 484 and 531) as the homologue of the protractor hyo- 
mandibularis in Acipenser, and of the levator maxillae superioris 
in selachians. He derives them, as he does those muscles, from 
the dorsal half of the superficial layer of the general constrictor 
of the mandibular arch (No. 124, p. 407). McMurrich, on the 
contrary (No. 76, p. 127), derives them from some part of the 
adductor mandibulae of selachians, that is, from a muscle that 
is developed, according to Vetter and Gegenbaur (No. 124, p. 
446), from the deeper layer of the general constrictor of the 
mandibular arch. Whatever their derivation may be, they seem 
to me to be the homologue of the muscle called by Vetter in 
selachians Addy. It seems impossible that they should be the 
homologue of the levator maxillae superioris, as Vetter sug- 
gests, or be derived from that muscle if, as I shall attempt to 
show, the muscle Zms!, in Amia, is the homologue of one or 
more of the spiracle muscles of selachians, the muscles called 
by Tiesing (No. 123, p. 92) the levator palpebrae nictitantis, 
retractor palpebrae superioris, and constrictor superficialis dor- 
salis /y. These muscles in selachians cross the outer surface 
of the levator maxillae superioris, while Zs!, in Amia, crosses 
the inner surface of the levator arcus palatini. 
