THE MYOLOGY OF AMIURUS CATUS. 345. 
porting maxilla, the muscle has extended farther forwards than in 
any other Teleosts hitherto described. The muscles are very mobile 
structures, modification being in them more frequent and more com- 
plete than in the nerves, «ce. 
The add. hyomand., add. operc. and lev. operc., are all very closely 
related, not only in position but also in innervation. They belonged 
originally to the same constrictor layer from which the add. arc. pal. 
developed, constituting the posterior part of it. The lev. opere. is a 
specialization of the superficial fibres of the most posterior portion— 
that portion from which also the add. operc. originated. These three 
muscles and the add. wre. pal. are comparable to the dorsal portion 
of the constrictor of the Elasmobranchs ; the geniohyoideus, hyohyoi- 
deus and portion of the intermand. being comparable tu its ventral 
portion. 
The Branchial Muscles.—The muscles supplied by the glossophary- 
ngeal and vagus are small in bulk when compared with those already 
discussed. In the Teleosts the muscles chiefly concerned in the re- 
spiratory act are not those belonging strictly to the branchial but 
those of the mandibular and hyoid arches. It is by means of these 
that the cavity of the mouth is increased, and thus an inflow of water 
produced, and it is by them also that the water is forced out below 
the opercular apparatus, passing in its way over the branchial fila- 
ments. Accordingly, we find the branchial muscles somewhat. retro- 
graded in bulk from the condition seen in the Elasmobranchs, and 
this retrogression has been accompanied by a corresponding increase 
in size and strength of the hyoidean and mandibular muscles. 
I regret exceedingly that I cannot give details in regard to the 
innervation of many of the muscles, but, nevertheless, there are 
certain points which may be indicated. Most of the muscles of the 
branchial arches may also be reduced to the constrictor type, however 
much they may be modified. In the first place the lev. brunch. are 
evidently the superior portions of the constrictor musculature, as are 
also the mm. trans. dors. and interarc. obl. dors. The latter have 
been slightly diverted from their constrictor direction, but as their 
name implies are still somewhat oblique. The lateral portion of the 
original constrictor has entirely aborted in Amiwrus, though in certain 
forms, as Hsox, muscles are found at the angles of the arches, «e., 
where the upper limbs join the lower. No such muscles could, 
however, be detected in Amurus. 
