46 



half. Shorter membranes transverse to this divide the muscles again into a series of 

 oblique flakes which are seen separating from one another in a boiled fish brought to 

 table. 



In a symmetrical fish the median skeletal partition formed by the vertebras and 

 their spines and the interspinous bones terminates at the back of the skull, but in the 

 sole it is extended still further anteriorly over the dorsal side of the skull to the 

 extremity of the snout. The attachment of the membrane to the skull runs at first 

 along the median dorsal line of the skull, that is, the morphological median line, but 

 anteriorly it runs to the left of this line. It crosses the base of the left frontal bone 

 and is continued alcng the edge of the larse left ectetlimoid and finally to the left edge 

 of the mesethmoid. '.riius, morphologically, the median skeletal partition is continued 

 forwards on the left side of the facial region ventral to the left eye, though actually 

 the anterior continuation is in the same plane as the main part of the partition. This 

 anterior continuation is of course due to the anterior development of the dorsal fin 

 Avhich is supported by it. 



Mtisculaiure. 



A general view of the muscles of the right side of the sole is given on Plate XII. 



The white parts in that draAving represent the white tendinous membranes, excepting 



some of the bones of the head which are smoothly shaded, and the fin-rays : the 



shading of fine lines indicates the muscles, the lines being drawn in the direction of 



the muscle-fibres. The principal muscles of the body are the great lateral muscles, 



one dorsal and one ventral, separated from one another by the longitudinal fibrous 



membrane already described as projecting from the centra of the vertebrae outwards 



to the skin. Each lateral muscle consists of a longitudinal series of folded plates or 



segments, separated from one another by the transverse membranes previously 



mentioned. The fibres in the muscle-segments run in an antero-posterior direction 



parallel to one another, and are attached at each end to the transverse membranes, or 



to the bones and membrane in the median plane of the body. The transverse fibrous 



membranes have a curious folded and twisted arrangement. The outer edge of each, 



as can be seen from the illustration, has the form of the letter S. Starting from the 



longitudinal lateral membrane it curves first anteriorly, tlien posteriorly, and finally 



runs anteriorly again, tluis forming two curves in opposite directiims and a larger outer 



portion running obliquely forwards. The membrane itself is deeply hollowed 



forwards in the region of the first curve, backwards in that of the second, so 



t' .at the inner edge of tlie membrane instead of being S shaped is Z-shaped. This 



inner edge of the transverse membrane is attached to the median bones and membrane 



in the following way : it runs first along a vertebral spine for a short distance, then 



suddenly turns ofT at an angle and runs directly backwards till it reaches the next 



spine behind, along which it runs outwards (dorsally or ventrally) for some distance, 



