ON THE ANATOMY OF AMPIIIOXL'S LANCEOLATUS. 381 



Muscular System. 



This system is highly symmetrical, consisting of a series 

 of lateral muscular bundles, corresponding in number, size, 

 and position, to the vertebras of the " chorda dorsalis." These 

 bundles have a general resemblance to the division of the 

 lateral muscles of the higher fishes. Each bundle consists of 

 a dorsal and ventral portion. The dorsal passes from the 

 lateral line, on a level with the vertebral column, backwards 

 and upwards ; the ventral passes from the same level, down- 

 wards and backwards. The inferior bundle is the longest ; 

 and both of them have a somewhat conical shape, and are 

 attached to the spinal column and skin by the aponeurotic 

 septa formerly described. The fibres of these muscles pass 

 respectively from before, obliquely upwards and downwards 

 almost, but not completely, in the direction of the muscular 

 bundle, along that portion of the trunk occupied by the 

 branchial portion of the intestinal tube. The ventral bundles 

 pass half-way over the dilated cavity, and terminate in blunted 

 extremities, which are attached to the skin, and to the walls 

 of the branchial compartment, so as to dilate it for the recep- 

 tion of sea-water. Beyond the anus the ventral bundles are 

 attached to each side of the fibrous septum above described, 

 meeting below in a sharp ridge. Between the anus and the 

 branchial cavity, where these muscles inclose the digestive 

 portion of the intestinal tube, they do not meet completely 

 below, but are connected by an aponeurosis, which forms a 

 strong tendinous arch at the point in front, where the muscles 

 separate more completely. The whole cavity of the trunk, which 

 is occupied by the intestinal tube, is lined by a fine aponeurotic 

 membrane, which, about the lower edge of the lateral muscles, 

 becomes muscular, and shuts in the whole of the inferior pari 

 of Hi.' trunk from the mouth to the tendinous arch formerly 

 described. This abdominal muscle consists of two layers 



