THE ARTICULATIONS OR JOINTS. 
ARTHROLOGY. 
By Davip HEpBurvy. 
Arthrology is that branch of human anatomy which treats of the articulations 
or joints. 
An articulation or joint constitutes a mode of union or connexion subsisting 
between any two separate segments or parts of the skeleton, whether osseous or 
cartilaginous, and having for its primary object either the preservation of a more 
or less rigid continuity of the parts joined together or else to permit 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 coextensive 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 likewise 
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 pany nega- 
tive. Thus there is uninterrupted union between the 
opposed surfaces of the bones joined together at the plane 
of the articulation, 7.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 i 
the term suture (Fig. 193) is applied. In the latter case, P16: 193. Vertical; Skomron 
the uniting medium is a plate of hyaline cartilage. Such ; 
priiculations are called synchondroses (Fig. 194). In all the synchondroses, and in 
many of the sutures, the uniting medium tends to disappear in the progress of 
Intervening 
membrane 
