114 PHILOSOPHY OF ZOOLOGY. 



of the sea urchin, (Echinus esculentus, L.) When the 

 thin edge of a flat bone covers that of another, the suture 

 is called squamons. It is very common in the bones of the 

 heads of fishes. In these three kinds of sutures, where 

 they occur in vertebral animals, the line of separation is 

 most distinct in youth, and gradually disappears in advan- 

 ced life, by the two bones becoming ossified into one. In the 

 kind of junction we are now to notice, this never takes 



place. 



When a pit in one bone receives the projecting extre- 

 mity of another, the junction is called Gomphosis, ( y o^<p$ 

 cunens) because the one bone is inserted like a wedge into 

 the cavity in the other. The teeth in man and other qua- 

 drupeds, and the hooks in the snout of the saw-fish, afford 

 good illustrations of this kind of junction. It is unknown 

 among the invertebral animals. 



There is another kind of immoveable articulation, exhi- 

 bited in the claws of cats, seals, and many other animals. It 

 consists in the one bone having a cavity, with a protuber- 

 ance at its centre, which receives another bone or hard part, 

 sheathing it at the margin, and projecting into its interior 

 at the centre. The claws are fixed in this manner on the 

 last phalanges of the fingers and toes of the above mention- 

 ed animals ; and thus have a bony cone and duplicature, 

 to give greater stability to their base. 



Amphiarthrosis is a mode of junction between bones, 

 by the intervention of a substance, softer and more plia- 

 ble, by means of which, a degree of motion is permitted, 

 limited by the extent of its flexibility. W T here two bones 

 are united by the intervention of cartilage, as is most fre- 

 quently the case, the junction is termed Synchondrosis, 

 (trv* cum v$g? cartilago.) In this manner the ribs are unit- 

 ed with the breast-bone, and the two sides of the lower jaw 

 with each other, in the vertebral animals. The motion in 



