ARTHKOLOGY.— DIFFERENT KINDS OF JOINTS 131 



Section II.— ARTHROLOGY. 



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 most instances some softer intervening 

 substance lies 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 sub- 

 stance (periosteum), admit of little or no perceptible movement. In 

 other instances of continuous union the extremities of the bones arc 

 placed at such a distance, and the iutervening substance (ligament or 

 cartilage) is so yielding, that bending or other movements- may take 

 place. But in the greater number of articulations the apposed surfaces 

 of bone are not united either directly or mediately with each other, but 

 are free, and covered with plates of smooth cartilage, the surfaces of 

 which fit accurately together, while the bones are held together by 

 ligamentous structures placed in the vicinity of the joints. In such 

 articulations the bones are capable of gliding or moving upon each 

 other, the extent and directions of such movements varying with the 

 shape of the opposed cartilaginous surfaces, and the form and attach- 

 ments of the ligamentous and other bands which unite them. It is 

 upon distinctions such as those now adverted to that the various kinds 

 of joints or articulations have been brought under the three classes of 

 Synarthrosis, Amphiarthrosis, and Diarthrosis. 



Synarthrosis means direct or immediate union, and comprehends 

 the joints with little or no motion. It is found chiefly in the various 

 forms of suture by which the bones of the head, excepting the lower 

 jaw, are united. The suture is serrated or dcntatcd when the contiguous 

 margins of the bones are subdivided or broken up into projecting 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 Avhich, as in the union of the temporal with the 

 parietal bone, the edges are thinned and bevelled, so that one overlaps 

 the other to a considerable extent. 



The Iiarmonic suture or harmonia is the term employed to denote 

 simple apposition of comparatively smooth surfaces or edges, as in the 

 case of the two superior maxillary bones ; and the term schmd//ksis is 

 applied to that kind of union in which one bone is received into a 

 groove in another, as occurs between the rostrum of the sphenoid bone 

 and the vomer. The impaction of the roots of the teeth in tlieir sockets 

 has likewise been reckoned among the articulations, though with 

 doubtful propriety, and has been designated by the term gomjjhosis. 



K 2 



