148 MUSCULAR SYSTEM. 



beneath or above the surface of the water. Here, as in 

 the naked cephalopods, there is a thin panniculus carnosus 

 immediately beneath the coloured skin of the mantle, the 

 fibres of which interlace to form a thin recticulate tunic. 

 The parietes of the mantle are chiefly composed of longitu- 

 dinal muscular fibres, with a thin external and transverse 

 layer. The external and internal muscles of the abdominal 

 fins in the naked species, both those which connect these 

 organs with the trunk, and those which move their free mar- 

 gins, are inserted into two thin longitudinal cartilaginous 

 scapular plates. The palleal muscles are not inserted into 

 the shell of the argonaute, nor into the internal dorsal shells 

 of the naked cephalopods, as they are in the nautilus. The 

 upper margin of the mantle is attached behind to the cepha- 

 lic cartilage in the sepiola and the octopus, but is free in sepia, 

 loligo, and loligopsis. The cavity of the abdomen is partially 

 divided by two strong and broad muscular bands extending 

 downwards and forwards from the base of the funnel to be 

 attached to the anterior parietes of the sac. These two 

 strong longitudinal muscular columns, between which the 

 rectum passes forwards to the base of the syphon, serve to 

 contract longitudinally the cavity of the mantle, to limit the 

 extent of its dilatations, and to retract the funnel. There are 

 other muscular bands passing down from the back part of 

 the head to the base of the funnel at its posterior part. The 

 folds of peritoneum, which attach the branchiae to the sides 

 of the abdominal cavity, have distinct muscular fasciculi, for 

 raising and retracting these organs. The whole muscular 

 parietes of the abdominal sac are firm, white, arid remark- 

 ably compact, and besides their transverse and longitudinal 

 muscular layers, there are oblique and straight short fibres, 

 which pass through their thickness from one surface to the 

 other. Within the abdominal cavity a distinct muscular 

 tunic embraces the whole liver and oesophagus as far as the 

 gizzard, and connects them with the upper and back part of 

 the trunk. The strongest and the largest muscles of the 

 naked cephalopods are those which are attached around the 

 head, connecting that part with the trunk behind, and with 

 the arms before. Strong muscular bands pass upwards from 

 the back and fore parts of the trunk, and expand into radiat- 

 ing fasciculi, which enter into the bases of the feet The 



