The permanent cartilages are of vari. ous kinds. We find them composing the external ear, external aperture of th e nos trils, and eye-lids. The larynx is entirely composed of this substance ; and the tra chea, withits branches, is furnished with cartilaginous hoops,by which these tubes are kept permanently open, for the ready passage of air to and fronf the lungs.
The bodies of the vertebrm are Joined by large masses of a peculiar substance ; partaking of the properties and appear. ance of cartilage and ligament, which allow of the motions of these parts on each other, without weakening the support that is afforded to the upper parts oleic body in general, and to the head in particular, by the vertebral column. These carti lages impart a great elasticity to the spine ; by which the effects of concussion from jumping, from falls, gm. are weakened, and destroyed, before they can be propa gated to the head. When the body has been long in an erect position, the com pression of these cartilages, by the supe rior parts diminishes the height of the person. T1; ey recover their former length, when freed from this przssure : hence a person is taller when he rises in the morn ing, than after sustaining the fatigues of' the day, and the difference has sometimes amounted to an inch.
Cartilagesare sometimes interposed be tween the articular surfaces of bones, where they fill lip irregularities, that might otherwise impede the motions of the part; and increase the. security of the Joint, by adapting the articular surfaces to each 'tithe r.
The articular s'iriares of bones are, in every Instance, covered by a thin crust of cartilage, having its sutface most exqui sitely polished, by which all friction in the motions of the joint is avoided, and the ends of the bones glide over each other with the most perfect facility.
Xemenclature of bones.—The processes or apophyses of bones bear different names, according to their figures. Hence we find them described under the terms of' head (roundish ball) ; condyle (a flat tened head); neck ; tuberosity; spine ; ts.c. others have particular names front supposed resemblances.
'The cavities or depressions of bones are called cotyloid, when deep ; glenoid, when shallow. Again, we have pits, fur
rows, notches, sinuosities, fossw, sinuses, foramina, and canals.
C'onnection of bonea.—Anatomists have divided these into three classes; Symphy sis, Synarthrosis, and Diarthrosis.
The term symphysis merely denotes the union of the conjoined bonesovithout any reference to peculiar form or motion ; hence it is divided, according to the means by which it is effected, into 1. Synchondrosis, where cartilage is the connecting medium : this is exempli fied in the junction of the rihs and ster limn ; of the bodies of the vertehrm ; and of the ossa pubis : 2. Synneurosis or syndesmosis ; where ligaments are the connecting bodies, as in all the moveable articulations: 3. Syssarcosis ; where muscles are stretched from one bone to another.
The synarthmsis, or immovable con junction of bones, consists of, 1. Suture ; where the bones are mutu ally indented, as if sewn together : 2. liarmonia ; where the conjunction is effected by plane surfaces: 3. Gomphosis ; v.-here one bone is fixed in another, as a nail is in a board. The teeth afford thc only specimen : 4. Schinclylesis ; where the edge of one bone is received into a groove in another: as the nasal plate of the ethmoid, in the vomer.
Diarthrosis, or moveable conjunction of bones. The conjoined parts of the bones am covered with a smooth cartilage, and connected by one or more ligaments. It has three subdivisions; ts:r.: 1. Enarthrosis, or ball and socket ; where a round head of one hone is re ceived into a cavity of another, and con. sapiently is capable of motions in all di rections ; 2. Arthrodia; where the cavity is more superficial, and much motion not allowed; 3 Ginglymus ; where the motions are restricted to two directions, as in the hinge of a door. The skeleton consists of an assemblage of all the bones in the body, excepting the os hyoides. It is said to be a natural ske leton when the bones are connected by means of their own ligaments or cartila ges ; an artificial one, when wire or other extraneous substances are employ ed.
It is divided into the head, trunk, and extremities.