VII 



MOLL USC A MUSCULATURE 



127 



mention the nuchal cartilage and the 

 cavity (p. 55). In the diaphragm, 

 over which the mantle depends, 



cartilages for locking the cleft of the mantle 

 i.e. in the posterior wall of the visceral dome, 

 there is in the Decapoda a cartilage near the 



funnel, the diaphragm cartilage. Finally must be mentioned a dorsal cartilage, 



It lies, posteriorly, on the anterior 



which is specially strongly developed in 

 border of the mantle, where the latter pro- 

 jects over the neck ; it bears the same 

 relation to the nuchal cartilage as does 

 the cartilaginous projection on each side of 

 the mantle to the cup-shaped socket at each 

 side of the base of the funnel or siphon (cf. 

 Fig. 80). 



In Sepia the dorsal cartilage is continued 

 in the shape of a cartilaginous rod running 

 up on each edge of the shell. The inner 

 edges of these rods have a groove into which 

 the edge of the shell fits, and thus form a 

 kind of fold round its lateral edges. 



In the Octopoda there is a cartilaginous 

 band on each side in the dorsal integument 

 which may correspond with the dorsal carti- 

 laginous rods in Sepia. It is possible that 

 the "internal shell" of the only Octopod 

 in which a shell is found, viz. Cirrho- 

 teuthis, is not in reality homologous with 

 the shell of the Decapoda, but corresponds 

 with the cartilaginous bands of Octopus 

 fused in the middle line. 



The (basipterygial) cartilages, univers- 

 ally found at the bases of the fins in the 

 Decapoda, complete the list. 



With regard to the musculature 

 of the Dibranchia, that of the mantle, 

 the fins, and the arms cannot be 

 described in detail. We note, how- 

 ever, that the pallial musculature 

 is principally attached to the shell 

 or to the dorsal cartilage, the fin- 

 musculature to the fin-cartilages, and 

 the brachial musculature to the an- 

 terior side of the cephalic cartilage, 

 and partly to the basi-brachial carti- 

 lage when such is present. 



The remaining musculature can be best explained with the assist- 

 ance of the accompanying diagram (Fig. 110), which represents the 

 musculature of Enoploteutlds. 



The strong paired depressor infundibuli (1) rises from the shell 

 on each side (or from the dorsal cartilage), and runs downwards and 

 backwards to the base of the funnel and to the cartilaginous socket. 

 From it spring most of the muscles of the anterior wall of the funnel. 



FIG. 110. Diagram of the more important 

 parts of the Dibranchiate musculature. 



Body seen from the left side. i>, Ventral ; <?, 

 dorsal; o, anterior; p, posterior ; 1, depressor 

 infundibuli; 2, retractor capitis lateralis; 3, 

 retractor capitis medianus ; 4, musculus col- 

 laris ; 5, adductor infundibuli ; 6, shell ; 7, 

 dorsal cartilage ; S, nuchal cartilage ; 0, cephalic 

 cartilage ; 10, mantle cavity ; 11, cartilaginous 

 socket of the locking apparatus on the posterior 

 wall of the visceral dome ; 12, corresponding 

 cartilaginous knob on the inner wall of the 

 mantle, which fits into 11 ; 13, funnel or siphon 

 (infundibulum) ; 14, diaphragm cartilage. 



