THE MYOLOGY OF AMIURUS CATUS. 331 
Tnnervation.—The fibres of each myomere are, of course, supplied 
by the spinal nerve corresponding to it segmentally. The supra- 
carinales are supplied by branches from the ramus lateralis trigemini. 
The muscular mass immediately in front of the dorsal fin is supplied 
by the dorsal branch of the fourth spinal, and the musculature 
anterior to that is supplied by branches from the ram. lat. trig., with 
which the rami dorsales vi. and iii. completely unite. The infra- 
carinales are supplied by branches arising from a plexus formed by 
the union of the ventral branches of certain spinal nerves. 
VII.—MUSCLES OF THE PECTORAL ARCH AND FIN. 
Certain muscles belonging partly to this arch, but acting princi- 
pally on others, have already been described, as, for instance, the 
hyopectoralis, and the pharyngo-hyoidei externus and internus. The 
muscles here to be considered are those which act principally on the 
arch, and those which move the fin. Of the former, the ‘ yreat ventral 
muscle,’ which acts as a retractor, has already been described. 
1. TRAPEZIvs. 
This muscle arises from the posterior portion of the lower surface 
of the pterotic, a few fibres also coming from the supraclavicle. It 
passes downwards, expanding as it goes, and is inserted into the base 
of the ascending portion of the clavicle, the more anterior fibres 
passing into the dense fascia which forms*the posterior wall of the 
branchial cavity. 
Innervation.—Twigs from main branch of first spinal nerve. 
Action.—It draws the pectoral arch upwards, and also makes 
tense the fascia into which the anterior fibres are inserted. 
In the forms described by Vetter this muscle does not apparently 
occur, that named trapezius by him being merely the superticial 
anterior portion of the dorsal trunk musculature, which extends 
between the posterior surface of the skull and the post-temporal and 
supra-clavicular bones The trapezius as here defined corresponds 
rather with that of the Hlasmobranchs. Stannius mentions its 
occurrence in some Teleosts. 
Owing to the modification of the anterior fin ray, whereby it can 
be fixed, and only lowered after a certain amount of rotation, the 
muscles which move it are different to a certain extent from those 
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