THE ARTICULATIONS OK JOINTS. 



SYNDESMOLOGY. 



By DAVID HEPBURN. 



Syndesmology is that branch of human anatomy which treats of the articulations 

 or joints. 



A junctura ossium (articulation or joint) constitutes a mode of union or con- 

 nexion subsisting between any two separate segments or parts of the skeleton, 

 whether osseous or cartilaginous. It has for its primary object either the 

 preservation of a more or less rigid continuity of the parts joined together, or else 

 the permission of a variable degree of mobility, subject to the restraints of the 

 uniting media. 



Classification of Joints. In attempting to frame a classification of the 

 numerous joints in the body, several considerations must be taken into account, 

 viz., the manner and sequence of their appearance in the embryo ; the nature of the 

 uniting media in the adult, and also the degree and kind of movement permitted 

 in those joints where movement is possible. 



In this way we obtain two main subdivisions of joints : 



(1) Those in which the uniting medium is co-extensive with the opposed sur- 

 faces of the bones entering into the articulation, and in which a direct 

 union of these surfaces is thereby effected. 



(2) Those in which the uniting medium has undergone more or less of interrup- 

 tion in its structural continuity, and in which a cavity of greater or less 

 extent is thus formed in the interior of the joint. 



To the first group belong all the immovable joints, many of which are only 

 of temporary duration ; to the second group belong all joints which possess, as their 

 outstanding features, mobility and permanence. 



SYNARTHROSES. 



The general characteristics of this group are partly positive and partly nega- 

 tive. Thus, there is uninterrupted union between the 

 opposed surfaces of the bones joined together at the plane 

 of the articulation, i.e. there is no trace of a joint cavity, 

 and further, there is an entire absence of movement. 

 Developmentally, these joints result from the approxi- 

 mation of ossific processes which have commenced from 

 separate centres of ossification, and therefore the nature 

 of the uniting medium varies according as the bones 

 thus joined together have originally ossified in membrane 

 or in cartilage. In the former case union is effected by 

 an interposed fibrous membrane continuous with, and 

 corresponding to, the periosteum. To such articulations 

 the term sutura (Fig. 287) is applied. In the latter case Fl - 287 - 

 the uniting medium is a plate of hyaline cartilage. Such 

 articulations are called synchondroses (Fig. 288). In all the synchondroses, and in 

 many of the sutures, the uniting medium tends to disappear in the progress of 



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