148 THE ARTICULATIONS IN GENERAL. 



bone, the edges are thinned and bevelled, so that one overlaps 'the other to 

 a considerable extent. Harmonic suture or harmonia is the term employed to 

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

 of the vertical plate of the palate and the superior maxillary bones ; and the term 



A. 



Fig. 171. SCHEME OF A SYMPHYSIS. 

 (Q. D. T.) 



Fig. 170. VARIOUS FORMS OF SUTURE. (G. D. T.) 

 A, dentated ; B, squamous ; C, harmonic ; D, grooved. B, C, and D, in section. 



grooved suture or schindylesis is applied to that kind of union in which one bone is 

 received into a groove in another, as occurs with the rostrum of the sphenoid bone 

 and the vomer. 



3. Symphysis. The bones are united by a plate or disc of fibro-carbilage of 

 considerable thickness, and of a more or less complex structure, as in the articula- 

 tions between the bodies of the vertebras, and 

 between the two pubic bones. 1 



4. Syndesmosis. The bony surfaces are 

 united by an interosseous ligament, as in the 

 lower tibio-fibular articulation. Union by in- 

 terosseous membrane is also a form of syndes- 

 mosis, in which, the bones being more widely 

 separated, the intervening ligament is extended 

 and assumes the membranous form. In the 

 hand and foot the lateral connections of many 

 of the carpal and tarsal, as well as of the metacarpal 

 and metatarsal bones are partly syndesmosis, the synovial 

 joints extending over only a small part of the adjacent 

 surfaces. 



Synchondroses and sutures are immoveable articula- 

 tions, but in symphyses and syndesmoses, which may be 

 classed together as partially moveable articulations, a 

 certain amount of play is allowed, varying in extent and 

 direction according to the thickness of the uniting sub- 

 stance and the nature of the other connections formed 

 by the articulating bones. 



B. DIARTHROSIS OR DISCONTINUOUS ARTICULATION. This division includes the 

 complete joints, with synovial cavities separating the articular surfaces of the bones, 

 and is attended with considerable yet varying degrees of mobility. In this form of 

 joint plates of cartilage cover the articular parts of the bones and present within the 

 joint free surfaces of remarkable smoothness, and these surfaces are lubricated by 

 the synovial fluid secreted from the delicate membrane which lines the fibrous 



Fig. 172. SCHEME OF A 



SYNDESMOSIS. (G. D. T. ) 



1 This form of articulation is sometimes regarded as a third primary division, under the name of 

 amphiarthrosis. 



