314 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
pose that originally it received a portion of the muscle, and that the 
arrangement now seen in Cyprinus, Barbus, and Perca, is the older 
one, that of Hsox and Amiurus being the later modification. 
2. Appuctor Textacuu.—(Pl. IIL., Fig. 1, and 2, AT.) 
On cutting through the insertion of the add. mand. and reflecting 
it, a muscle is exposed which is apparently characteristic of the 
Siluroids. It arises from the outer surface of the metapterygoid, its 
upper portion being covered by the /ev. arcés palatini. It runs for- 
ward beneath the add. mand., forming the inferior boundary of the 
orbit and being crossed by the fifth nerve. Anteriorly it becomes. 
tendinous, the tendon near its insertion dividing into two slips, be- 
tween which the nerve supplying the tentacle passes. One of these 
slips is inserted into the upper, the other into the lower border of the 
base of the maxilla, which encloses the proximal portion of the 
tentacle. 
Innervation.—It is supplied by a branch of the same nerve that 
supplies the deeper portions of the add. mand. 
Action.—It draws the tentacle backwards towards the middle line, 
opposing the anterior portion of the add. arcés palatini. 
The position and innervation of this muscle leads to the conclu- 
sion that it isa part of the add. mand. which has been separated off 
for a particular purpose. It does not, however, compare with any 
of the three parts of that muscle in Barbus or Perca, nor even with 
the fourth part, which is sometimes present, as in Cyprinus, since~ 
this is formed by a division of the superficial portion. Since the 
osseous support of the long tentacle is the maxilla, this muscle 
bears a certain amount of analogy to the superficial portion of the 
add. mand., but it cannot be its homologue. The relation of the 
maxilla to the tentacle was probably secondary, and since the power 
of moving the tentacle would always have been an advantage it is 
probable that originally the muscle was inserted into the tentacular 
cartilage, its insertion into the maxilla only occurring after that bone 
had commenced to be a support and had enclosed the base of the 
tentacle. There are two theories which will account for the presence of 
this muscle. (1) It may be a new structure evolved for a particular 
purpose, or (2), it may be the representative of a muscle present in 
ancestral forms but which has disappeared in all the Teleostet 
hitherto examined. If the latter is the correct explanation, one 
