440 



CEPHALOPODA. 



pectations 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 sys- 

 tem 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 ganglionic 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 mus- 

 cular system in different regions of the body. 



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 (fig. 215) embraces the oeso- 

 phagus with a cartilaginous ring, encases the brain, affords passage 

 to the optic nerves, and gives off orbital plates for the protection of 

 the eyes. This cartilage likewise gives a firm origin to the muscles 

 of the locomotive tentacula 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, there- 

 fore, it claims to be considered 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 appendages of that description offer, un- 

 doubtedly, the rudiments of those portions of the skeleton that 

 sustain the locomotive limbs of quadrupeds. 



(482.) 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. 



On slitting up the mantle of a Calamary (Loligo) along the me- 

 sial 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 



