<§<^ 236, 237, 238. the cephalopoda. 275 



Although it must be supposed that the calcareous matter of this shell ia 

 secreted bj the internal surface of the dorsal cavity, yet the thin fibrous 

 membrane which lines this last, is without a glandular structure. 



CHAPTER III 



MUSCULAR SYSTEM AND ORGANS OF LOCOMOTION. 



§ 236. 



The muscular system of the Cephalopoda is highly developed. Its prim- 

 itive fibres are smooth, but are not so diversely interlaced as with the other 

 Mollusca. These fibres are usually parallel, and the fasciculi which they 

 form, are of equal thickness. When isolated, they often show a zigzag ten- 

 dency, which, probably, belongs also to their state of contraction. The 

 fasciculi are very compactly bound together in one direction by a cellular 

 tissue, and, in this manner, form clearly-defined, long, flat muscles. 



§237. 



The mantle of the Cephalopoda has a very distinct layer of circular 

 fibres.'^' From the internal surface of the sac which it forms, arise, in the 

 dorsal region, two pairs of large cylindrical muscles. One pair of these 

 passes in front and is extended into the walls of the base of the funnel ; 

 the other pair extends to the posterior part of the neck, and is inserted 

 partly into the cephalic cartilage, and partly at the base of the arms. The 

 other muscles, which are thinner, arise from the sides of the cervical carti- 

 lage, and are inserted upon the funnel.^-' By means of a part of this mus- 

 cular apparatus, these animals can vigorously contract the cavity of the 

 mantle and the funnel, and, by tightly embracing the neck and base of the 

 funnel with the border of the mantle, can eject, through the orifice of this 

 last, the liquids contained in the cavity of the body. With many species, 

 these muscular contractions serve, also, as a means of a backward locomo- 

 tion in the water. 



§ 238. 



The principal locomotive organs of the Cephalopoda are the arms fixed 

 upon the cephalic cartilage ; they serve also as prehensile organs. Each 

 of these consists of a tubular axis composed of a dense cellular tissue, of 

 muscular fibres radiating towards the surface, between which are inter- 



1 Tliis muscular layer is incomplete with Sepia trunk and the head of Cephalopoda may be found 



— being wanting in the dorsal portion of the iu Cuvier, loc. cit. p. 9 ; Hrandt, loc. cit, p. 303, 



ma-ntle. and especially in £)eWe C/u'aje, Memor. IV. p. 72, 



-' A very full description of the muscles of the and Descriz. &c., I. p. 21. 



