THE MYOLOGY OF AMIURUS CATUS. 331 



Innervation. — 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 ii. and Hi. 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 interims. The 

 muscles here to be considered are those which act principally on the 

 arch, and those which move the fin. Of the former, the ' great ventral 

 muscle,' which acts as a retractor, has already been described. 



1. Trapezius. 



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. 



1 1 (.nervation. — 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 Yetter this muscle does not apparently 

 occur, that named trapezius by him being merely the superficial 

 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 Elasmobranchs. 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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