530 



CEPHALOPODA. 



Fig. 216. 



Muscles of the Poulp, Octopus Vvlgaru. 



Fasciculi of muscular fibres (b, b, 216,) are 

 continued from the ventral pair of feet and the 

 back part of the cranium, across^ the base of 

 the funnel to the muscular septum, which 

 divides longitudinally the branchial cavity. 

 Other fibres descend to join the muscular tunic 

 enveloping the liver and esophagus (d, d) ; 

 but the fibres of this part rise principally from 

 the posterior part of the cephalic cartilage. 



The septum of the branchial chamber above- 

 mentioned is the strongest and most complete 

 in the genus Eledone, where, with the excep- 

 tion of a very small part of its posterior termi- 

 nation, it is muscular throughout.* In the 

 Poulp, in which this septum (c, Jig. 216) is 

 well described by Cuvier as the " bride ante- 

 rieure qui lie la bourse a la masse viscerale," 

 a greater proportion of the posterior part is 

 membranous. In the Argonauta the muscular 

 part of the septum is reduced to two narrow 

 and delicate fasciculi, which arise from the 

 back part of the cranial cartilage, descend ob- 

 liquely forwards, intercept the termination of 

 the rectum and ink-duct, to which they serve 

 as a sphincter, and then expand in the vertical 

 direction to be inserted along the middle line 

 of the inner surface of the anterior part of the 

 mantle. A membrane is continued from the 

 upper margin of the muscular septum to within 



* See Cams' original figure, Vergleich. Zooto- 

 mie, pi. iv. fig. 4, g, in Octopus ( Eledona) Mos- 

 chatus. 



a short distance of the anterior margin of the 

 mantle, and another from the lower margin ex- 

 tends downwards, and terminates opposite the 

 base of the gills ; the branchial chambers in- 

 tercommunicate both above and below this 

 septum. In Sepiola the muscles corresponding 

 to the " bride anterieure" of the Octopus are 

 developed in the same degree as in the Argo- 

 naut, arising not from the back of the funnel, 

 but from the cranial cartilage ; the septum is 

 completed below by membrane. In the Cuttle- 

 fishes and Calamaries these muscles and the 

 septum of the branchial chamber are wanting. 



The muscular parietes of the funnel are 

 formed by an external longitudinal ( e) and an 

 internal transverse (f) layer, strengthened by the 

 insertion of the extrinsic muscles of this part. 

 The principal of these are the lateral muscles 

 (g, Jig. 216,) which in the Poulp take their 

 origin from the capsules of two small styles, 

 hereafter to be described, at the sides of the 

 mantle, and are inserted into the sides of the 

 funnel and the muscular tunic of the liver. In 

 the Cuttle-fishes and Calamaries they are at- 

 tached to the cartilaginous articular cavity at 

 the sides of the base of the funnel, as well as 

 to its fleshy parietes. 



These muscles serve to retract and depress 

 the funnel; it is raised and drawn forwards by 

 two pair of muscles (h) which descend from 

 the under and lateral parts of the head to be 

 inserted into its back part. But neither of 

 these muscles pass through a sheath, as do the 

 corresponding muscles in the Nautilus. 



A pair of muscles, whose important charac- 

 ter is only perceived by tracing them through 

 their successive stages of development to the 

 Nautilus, are those small fasciculi which Cuvier 

 terms " la bride laterale qui joint la bourse a 

 la masse viscerale." (i.) They arise in con- 

 junction with the fibres of the fleshy tunic of 

 the liver, but soon quitting these, extend, as 

 distinct fasciculi, downwards and outwards, 

 being perforated in their course by the great 

 lateral nerve, and are inserted into the upper 

 part of the capsule of the rudimental shell, 

 which the styles above-mentioned represent. 

 In the Sepia they are proportionally larger, 

 corresponding to the greater development of 

 the shell. They are not inserted, in the Octo- 

 pus, into the cartilaginous substance of the in- 

 closed style ; nor, in the Sepia, into the calca- 

 reous substance of the cuttle-bone; neither 

 are they attached to the calcareous matter of 

 the shell in the Nautilus, where they acquire 

 their maximum of development. They termi- 

 nate in this, as in the preceding genera, in the 

 epidermic capsule of the shell, which has a 

 much closer and more intimate adhesion to 

 the testaceous substance in the Nautilus than 

 to the internal rudiment of the same part in the 

 naked Cephalopods. 



It is well known that zoologists are divided 

 in opinion as to whether the shell called Argo- 

 nauta is formed by the cephalopod which in- 

 habits it or not. Having traced out the mus- 

 cles in the naked Cephalopods which are ana- 

 logous to those of the shell in the Nautilus, we 

 next examined the Oci/thoe, with the view of 



