ARTHKOLOGY. 



By Gr. D. THANE, 



THE ARTICULATIONS IN GENERAL. 



VARIOUS FORMS OF JOINTS. The name of articulation, synonymous with joint, 

 is given in descriptive anatomy to the connection subsisting in the recent skeleton 

 between any of its denser component parts, whether bones or cartilages. In all in- 

 stances some softer substance intervenes between the bones, uniting them together, 

 or clothing the surfaces which are opposed ; but the manner in which the several 

 pieces of the skeleton are thus connected varies to a great degree, both as to the nature 

 of the uniting substances, and the extent of movement which they allow. In some 

 instances, as in the cranial bones, the closeness of the apposition/the unevenness of the 

 fitting surfaces or edges, and the small amount and dense nature of the intervening 

 substance admit of no perceptible movement. In other instances of continuous union 

 the extremities of the bones are placed at such a distance, and the intervening 

 substance is so yielding, that bending or other movements may take place. But in 

 the greater number of articulations the opposed surfaces of bone are not united with 

 each other, but are free, and are covered with plates of smooth cartilage, the 

 surfaces of which fit more or less accurately together, while the bones are held 

 together by ligamentous structures placed in the vicinity of the joint. In such 

 articulations the bones are capable of gliding or moving upon each other, the extent 

 and directions of the movements varying with the shape of the opposed cartilaginous 

 surfaces, and the form and attachments of the ligamentous and other bands which 

 unite them. According to differences of the kind now adverted to the various 

 articulations of the body are classified as follows : 



A. SYNARTHROSIS OR CONTINUOUS ARTICULATION. The adjacent osseous 

 surfaces are directly united by some interposed substance. 



1. Synchondrosis. A thin layer of cartilage is interposed between the bones, to 

 which it adheres closely on each side. This articulation is essentially of a transitory 

 nature, being usually converted into bony union (synos- 



tosis) before adult age is reached. It occurs between 

 the different portions of bones developed in cartilage, 

 as in the vertebrae, in the long bones of the limbs, and 

 in the bones of the base of the skull. 



2. Suture. In this form of articulation, which is 



met with only in the skull, the bones are separated by Fig. 169. SCHEME OP A 

 a thin layer of fibrous tissue continuous with the peri- SYNCHONDROSIS. (G. D. T.) 

 osteum. It also exhibits a tendency to pass over 



into synostosis, but in a variable degree at different places, and at a later period 

 than the cartilaginous union (p. 62). The suture is serrated or deniated when 

 the contiguous margins of the bones are subdivided or broken up into pro- 

 jecting points and recesses by which they fit very closely to one another, 

 as in the borders of most of the tabular bones of the cranium. The squamous 

 or scaly suture is that in which, as in the union of the temporal with the parietal 



VOL. II. L* 



