568 CEPHALOPODA. 



animals possessed of an internal bony framework ; and our expectations 

 in this particular will be found on investigation to be well-grounded. 

 It is, in fact, in the CEPHALOPODA, the highest of the molluscous classes, 

 that the rudiments of an osseous system for the first time make their 

 appearance ; not, indeed, as yet composed of perfect bone, but formed 

 of cartilaginous pieces, some being so disposed as to protect the gan- 

 glionic mass above the oesophagus, which now from its size well deserves 

 the name of brain, whilst others serve to afford bases of attachment to 

 the muscular system in different regions of the body. 



(1524.) The most important piece met with in the cartilaginous 

 skeleton of the Cuttle-fish encloses and defends the brain, and therefore 

 is most appropriately called the cranial cartilage, being the corre- 

 spondent, both in position and office, with the cranium of a vertebrate 

 animal. This rudimentary cranium embraces the oesophagus with a 

 cartilaginous ring, encases the brain, affords passage to the optic nerves, 

 and gives off orbital plates for the protection of the eyes. The cranial 

 cartilage likewise gives a firm origin to the muscles of the locomotive 

 tentacola appended to the head, and, moreover, contains within its 

 substance an auditory apparatus, presenting the earliest condition of 

 an organ of hearing such as is met with in the vertebrate division of 

 the animal kingdom ; in every respect, therefore, it claims to be con- 

 sidered as the first appearance of a skull. Another broad cartilage is 

 imbedded among the muscles at the base of the funnel ; and two distinct 

 plates, situated in the lateral fins of such species as possess append- 

 ages of that description, offer, undoubtedly, the rudiments of those por- 

 tions of the skeleton that sustain the locomotive limbs of quadrupeds. 



(1525.) But while we thus see in the CEPHALOPODA the earliest form 

 of an internal osseous skeleton, we cannot be surprised to find these 

 mollusks still retaining, at the same time, the tegumentary calcareous 

 shell or epidermic skeleton of inferior animals. 



(1526.) On slitting up the mantle of a Calamary (Loligo) along the 

 mesial line of the back, it is found to contain a large cavity, wherein 

 is lodged a long plate of horn, called the gladius, which in shape might 

 be not inaptly compared to the head of a Roman spear. This enclosed 

 horny substance, notwithstanding the dissimilarity of texture, is, in 

 fact, strictly analogous to the enclosed shell of the Slug, described in a 

 former page ; and its growth is effected in the same manner, namely 

 by an exudation of corneous material from the floor of the chamber 

 that contains it ; and this horny secretion, hardening as it is deposited 

 layer by layer, adds to the dimensions of the gladius as the growth of 

 the animal proceeds. Several of these plates may be produced in suc- 

 cession ; and in old individuals it is not uncommon to find two or three 

 enclosed in the same cavity, and placed one behind the other that 

 nearest the visceral aspect of the chamber being the most recently 

 formed. These rudimentary shells have no connexion whatever with 



