524 



CEPHALOPODA. 



Fig. 211. 



Genus ELEDONE, Leach. The arms pro- 

 vided with a single series of sessile 

 acetabula. 



Ex. Eledone cirrosa, Leach. 

 Internal cartilaginous parts, or Endo- 

 skeleton. In the Gasteropodous Mollusks the 

 cerebral or supra-cesophageal ganglions are pro- 

 tected by a dense membrane which has been 

 compared to a dura mater, but which may be 

 regarded with more propriety as representing 

 the membranous condition of the skull in the 

 embryo of the vertebrate animal ; and which, 

 in fact, assumes a cartilaginous texture in some 

 of the higher organized Pectinibranchiata, 

 forming in them the unquestionable rudiment 

 of a true internal skeleton. 



In the present class a thick cranial cartilage 

 not only protects the cephalic masses of the 

 nervous system ; but it is enlarged and extended 

 in different directions, so as to afford a basis of 

 attachment to the principal muscular masses of 

 the body : thus fulfilling the second important 

 function of an internal skeleton. 



In the Nautilus it consists of one principal 

 cartilage, (fg. 211,) which is situated on the 



ventral aspect of the 

 oesophagus ; two pro- 

 cesses (a a) extend 

 from the posterior or 

 dorsal angles on each 

 side of the oesophagus 

 as far as the optic gan- 

 glions. A deep semi- 

 circular groove (6) 

 extends along the an- 

 terior part of these 

 processes for the lodg- 

 ment of the optic 

 ganglions and the an- 

 terior nervous collar 

 surrounding the oeso- 

 phagus. Two other 

 processes (c c) arise 

 from the ventral angles 

 of the cartilage and 

 give support to the sides of the base of the 

 funnel. A middle process is extended some 

 way between the two great muscles which are 

 inserted into the shell. The central part or 

 body of the cartilage (d) is excavated for the 

 reception of the venous blood returned from 

 the head and funnel, and from this sinus the 

 great dorsal vein commences. 



In the Dibranchiate Cephalopods the inter- 

 nal cartilaginous skeleton consists of a greater 



Gudltieri, when he first separated it generically 

 from the Chambered Nautilus. In either case, as 

 the grounds for constituting the new family of Oc- 

 topoda now proposed are derived from important 

 organic differences, as manifested in the structure 

 of the funnel and the branchial hearts, the claims 

 of the Cephalopod to form the type of such a group 

 would not be destroyed by the proof of the shell 

 forming no part of its structure. We cannot, how- 

 ever, retain both the genera Argonauta and Ocy- 

 thoe, as in the Fatnilles Naturelles d-i Reyne Animal 

 of Latreille, p. 168; since, if the sl.ell in question 

 be not secreted by the Cephalopod, its analogy to 

 that of the Carinaria would indicate its real con- 

 structor to belong to the Heteropodous Mollusks. 



Internal Cartilage or 

 Skeleton of the Nautilus. 



number of pieces, and has a more important 

 share in the organization and functions of the 

 animal. We shall describe it principally as it 

 exists in the Cuttle-fish (Sepia Officinalis). 



The cranial cartilage (A, Jig. 212) is no 

 longer limited in its position to the under side 

 of the oesophagus, but completely surrounds 

 that tube, which, together with the inferior sali- 

 vary ducts, and the cephalic branches of the 

 aorta, traverses a narrow passage in the centre. 

 It is expanded above into a cavity, which en- 

 closes and protects the brain ; while, below the 

 oesophagus, the dense cartilage is excavated to 

 form the two vestibular cavities of the organ 

 of hearing ; at the sides it is developed into 

 broad and thick concave processes, which form 

 the back part of the orbits. 



In the subjoined figure A is the cranial car- 

 tilage as seen from above : 



a is the superior part which protects the brain. 



b, b, are the two large optic foramina. 



c, c, the posterior and inferior thick ex- 

 panded orbital process. 



d, d, the thin and long anterior and inferior 

 cartilage which supports the eye-ball, and is 

 analogous to the cartilaginous eye pedicle of 

 the Rays and Sharks : these processes are com- 

 pared by Meckel to the superior maxilla ; they 

 do not exist in the Octopods, and are compa- 

 ratively much smaller in the Calamaries than 

 in the Cuttle-fish. 



e, the anterior aperture of the canal through 

 which the oesophagus passes. 



_/, a process, continued from the anterior 

 part of the cranial cartilage, which expands 

 into a broad transverse plate, with a slight con- 

 cavity directed forwards, and gives attachment 

 to the muscles of the arms: this cartilage 

 Meckel compares to the lower jaw, but the 

 analogy is not more satisfactory than in the 

 preceding instance. 



The infundibular or nuchal cartilage (B), 

 which is a process of the cranial cartilage in 

 the Nautilus, is in the Dibranchiates, and es- 

 pecially the Cuttle-fish, a distinct piece, of 

 large size, and of a flattened triangular figure, 

 situated above the base of the funnel, with its 

 apex directed forwards and its posterior angles 

 turned backwards : it has a moderately deep 

 furrow along the middle of its upper surface. 

 In the Sagittated Calamary this important car- 

 tilage consists of three portions, a middle elon- 

 gated one, having on its dorsal surface a mesial 

 longitudinal groove, and two lateral longitudinal 

 ridges which are adapted to a corresponding 

 ridge and two grooves in the under part of the 

 sheath of the gladius, which sheath here assumes 

 a dense cartilaginous consistence : from the an- 

 terior extremity of the middle nuchal cartilage 

 two flattened cartilages extend outwards and 

 backwards, and then curve slightly inwards. 

 These correspond to the dilated base of the carti- 

 lage in the Sepia, protect the great lateral nerves 

 of the mantle, and give origin to the lateral 

 muscles which are perforated by the nerves. 



On each side of the base of the runnel 

 there is a smooth oblong articular cavity which 

 is formed by a distinct cartilage (C); it is 

 adapted to receive a corresponding cartilagi- 



