CEPnALOPODA. 609 



situated on the dorsal part of tlie mantle, near the anterior end of 

 the internal shell : in Loligo^ there is a second long rhomboid dorsal 

 cartilage. The infundibular cartilage, which is a process of the 

 cranial one in the Nautilus, is a distinct piece in the Dibraiichiata. 

 It is of a large size, and of a flattened triangular figure in the cuttle- 

 fish, in which it is situated above the base of the funnel. It consists 

 of three distinct portions in the Calamarj. On each side the base of 

 the funnel there is a smooth oblong articular cavity, formed by a 

 distinct piece of cartilage, which is articulated with a corresponding 

 cartilaginous prominence from the inner surface of the side of the 

 mantle. These cartilaginous joints of the funnel vary in shape in 

 the different genera : they are wanting in the Octopus. The lateral 

 fins of the Decapoda are each supported by a narrow flattened 

 elongated cartilaginous plate, which forms the medium of attachment 

 of the powerful muscles of those fins. These appear to be homologous 

 with the parial fins of fishes ; but as they are not fixed to a vertebral 

 column, their position is variable ; in the Rossia, for example, they are 

 situated near the anterior part of the body ; in the Loligo, they are 

 placed at the posterior extremity ; in the Sepia they extend, like the 

 great pectoral fins of the Rays, along the whole side of the body. In 

 the Octopods the mantle-fins and their cartilages are wanting, except 

 in the anomalous genus Sciadephorus in which they are attached to 

 the anterior part of the sides of the mantle. 



The sole locomotive organs in the ordinary Octopods and the sole 

 prehensile organs in all the Dibranchiates are the appendages deve- 

 loped from the head, termed " arms," " feet," " tentacles," and " pro- 

 boscides." They have no true homology with the locomotive members 

 of the Vertebrata, but are analogous to them, inasmuch as they relate 

 to the locomotive and prehensile faculties of the animal.* 



The eight arms of the Octopus commence by a hollow cone of 

 muscular fibres attached by a truncated apex to the anterior part of 

 the cephalic cartilage. The fibres are for the most part oblique, and 

 interlace with one another in a close and compact manner, as the cone 

 advances and expands to form the cavity containing the mandibulate 

 mouth, at the anterior extremity of which they are continued forward, 

 and separate into eight distinct portions which form the arms. The 

 development of the eight external arms bears an inverse proportion 

 to that of the body ; they are longest in the short round-bodied Octopi, 

 and shortest in the lengthened Calamaries and Cuttle-fishes, in which 

 the two elongated retractile tentacles are superadded by way of com- 



* Geoffroy St. Hilaire regarded the cuttle-fish as a vertebrate animal bent double, 

 with the approximated arms and legs extending forwards : a similar comparison 

 may be found in Aristotle. 



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