17 



anterior and outer part of this skeleton. They are so densely interwoven as to 

 preclude the possibility of a description of their exact course or arrangement ; 

 the most external, however, evidently affect a longitudinal direction, and the 

 fibres of the internal layer are transverse or circular. 



The great muscles of the shell (/f. k. fig. 2. pi. 3 ; e. pi. 5.) arise from the 

 whole posterior part of this cartilaginous mass, which thus becomes a firm bond 

 of union between the exterior organs of locomotion and the powers employed to 

 drag on the heavy shell behind. These muscles are an inch and a half in length, 

 two inches in depth, and half an inch in thickness ; they are convex on the out- 

 ward aspect, and slightly concave towards the viscera, where they are pei'forated 

 by the ramifications of the nutrient arteries, and by numerous nerves (/. /. pi. 7.). 

 Tliey pass outwards, and as they diverge are connected along their ventral 

 margins by a layer of transverse muscular fibres (m. fig. 2. pi. 3.), which sepa- 

 rates the branchial from the abdominal cavity. Their terminations are obliquely 

 truncate, and form the lateral oblong surfaces covered by the horny substance 

 above described {g. pi. 1 ; I. fig. 2. pi. 3.) ; and by means of that substance they 

 are attached to the sides of the last chamber of the shell, at the distance of half 

 an inch from the septum or floor of the cavity. 



In tracing these muscles through the higher genera of Cephalopoda, they were 

 found invariably in relation to the rudimentary shell ; proportioned to its various 

 degrees of development, and where it was altogether wanting, scarcely exhibiting 

 a trace of their existence. In Octopus, for example, they are partly continued 

 from the longitudinal fibres at the base of the arms, and partly derived from the 

 cephalic cartilage ; they pass down behind the lateral crura of the funnel, are 

 there perforated by the nerve of the ganglion stellatum ; become attached to the 

 sides of the mantle, and are ultimately inserted at the anterior part of the cap- 

 sules of the friable styles. In Cuvier's Memoir e sur le Poulpe they are marked 

 /. /. fig. 1. & 2. pi. 1 ; k. k. fig. 1. pi. 4. and are termed respectively, " la bride 

 laterale qui joint la bourse a la masse viscerale". p. 13. The analogous muscles 

 in Loligo are larger, and derive more of their fibres from the cephalic cartilage ; 

 they have the same course as in Octopus, are similarly perforated by the nerve 

 above mentioned, and are lost in the sides of the capsule of the horny pen. In 

 Sepia also they are more developed, are shorter and thicker than in Octopus, 

 are also pierced by the nerve of the ganglion stellatum, and are inserted in the 



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