1^0 



ON THE BONES, ET€. 



beautiful paper-nautilus, and still more beautiful pearl-nautilus (argonauta 

 and nautilus tribes,) and which hence obtain no inconsiderable portion of 

 that lightness which enables them, with their extended sails, to scud so 

 dexterously before the wind. In the calamary (sepia Loligo) we meet 

 with an approach towards the same contrivance, in a kind of lealy plate 

 introduced mto the body of the animal ; and even m the cloak of the slug 

 tribe we trace something of the same sort, though proportionabiy snialler, 

 and verging to the nature of horn. 



Generally speakmg, the bones grow cartilaginous towards their extre- 

 mities, and the muscles tendinous ; by which means the lieshy and osseous 

 parts of the organs of motion become assimilated, and fitted for that inser- 

 tion of the one part into the other upon which their mutual action depends. 

 The extent and nature of the motion is determined by the nature ol the 

 articulation, which is varied with the nicest skill to answer the purpose in- 

 tended. In ostraceous worms the only articulation is that of the hinge : 

 in the cancer tribes the tendon is articulated with the crust, whence the 

 wonderful strength and activity of the claws ; and it is articulated in a simi- 

 lar manner with the scaly plates of some species of the tortoise. In insects 

 the part received and the part receiving form each a segment of a sphe- 

 roid ; whence the motion may be either rotatory or lateral, at pleasure. 

 In mammalian animals the lower jaw only has a power of motion ; but in 

 birds, serpents, and fishes the upper jaw in a greater or less degree possesses 

 a similar power. 



The motion of serpents is produced, according to Sir Everard Home, 

 by their ribs, which for the most part accompany them, not only as organs 

 of respiration, but from the hind extremity to the neck, and are possest of 

 a peculiar power of motion by means of necuiiar muscles. " The vertebrae 

 are articulated by ball and socket-joints (the ball being formed upon the 

 lower, and the socket on the upper one), and have therefore much more 

 extensive motion than in other animals." In the draco volans the skeleton 

 of the wings is formed out of ribs which " are superadded for this pur- 

 pose, and make no part of the organs of respiration ; the ribs in these ani- 

 mals appear to work in succession, like the feet of a caterpillar." 



The TEETH vary m their form and position almost as much as the bones. 

 Where jaw-bones exist they are usually fixt immoveably in their sockets ; 

 but in some animals a few of them are left moveable, and in others the 

 whole. The mus maritimus^ or African rat, the largest species of this 

 genus which has hitherto been discovered, and seldom less than a full- 

 sized rabbit, hUs the singular property of separating at pleasure to a con- 

 siderable distance the two front-teeth of the lower jaw, which are not less 

 than an inch, and a quarter long. That eJegant and extraordinary crea- 

 ture the Kangaroo, which, from the increase that has lately taken place in 

 his Majesty's gardens at Kew, we may soon hope to see naturalized in our 

 own country, is possessed of a similar faculty. And the hollow tusks or 

 poisoning fangs of the rattlesnake, and other deadly serpents, are situated 

 in a peculiar bone on each side of the upper jaw, so articulated with the 

 rest, that the animal can either depress or elevate them at his option. In 

 a quiescent state they are recumbent, with their points directed inwards ; 

 but whenever ttie animal is irritated he instantly raises them ; and at the 

 moment they inflict a wound, the poison, which lies in the reservoir imme- 

 diately below, is injected through their tubes by the act of pressure itself. 



In the shark and ray genera the whole of the teeth are moveable, and 

 lie imbedded in jaw-cartilages instead of in jaw-bones, and like the fangs of 



