300 



THE ARTICULATIONS OK JOINTS. 



Intervening 



hyaline 



cartilage 



Fia. 



THE OCCIPITO-SPHENOID SYN- 

 CHONDROSIS. 



ossification, and thus the plane of articulation becomes obliterated, so that direct 

 structural continuity between the osseous segments takes place. The primary 



features common to all synarthroses are (a) continuous 

 and direct union of the opposing surfaces; (&) no joint 

 cavity ; (c) no movement. 



Sutura. This form of synarthrosis is found only in 

 connexion with the bones of the skull. In a large 

 number of cases the bones which articulate by suture 

 present irregular interlocking margins, between which 

 there is the interposed fibrous membrane to which refer- 

 ence has already been made. When these interlocking 

 margins present well-defined projections they are said to 

 form a sutura vera (true suture) ; on the other hand, when 

 288. SECTION THROUGH the opposed surfaces present ill-defined projections, or 

 even flat areas, they are described as sutura notha 

 (false suture). In each of these subdivisions the particular 

 characters of the articulating margins are utilised in framing additional descriptive 

 terms. Thus true sutures may possess interlocking margins whose projections are 

 tooth-like (sutura dentata), e.g. in the interparietal suture ; saw-like (sutura serrata) 

 (Fig. 289), e.g. in the interfrontal suture ; ridge-like, or comparable 

 to the parallel ridges on the welt of a boot (sutura limbosa). 

 Similarly false sutures may articulate by margins which are scale- 

 like (sutura squamosa), e.g. in the squamoso-parietal suture ; or by 

 rough opposed surfaces, sutura harmonia, e.g. in the suture between 

 the palatine processes of the maxillary bones. There is one 

 variety of synarthrosis which, in the adult, can scarcely be called a 

 suture, although the differences are of minor importance, viz., 

 schindylesis, which is an articulation between the edge of a plate- 

 like bone, such as the rostrum of the sphenoid, and the cleft in I 

 another, such as the vorner. 



Synchondrosis. Illustrations of this group can be found only ] 

 in the young growing individual, because as age advances and 

 growth ceases, the process of ossification affects the hyaline cartilage which con- 

 stitutes the uniting medium, and the plane of articulation disappears. Under this 

 heading we may include the planes of junction between all epiphyses and the 

 diaphyses to which they severally belong. The occipito- sphenoid (Fig. 288) and 

 the petro-jugular articulations in the base of the skull provide other well-marked 

 examples. 



289. SUTURA 

 SERRATA. 



AMPHIARTHROSES DIARTHROSES (MOVABLE JOINTS). 



The leading features of this group are capability of movement and permanence. 

 In very few instances do such joints ever become obliterated under normal con- 

 ditions. Determining their permanence, and regulating the amount of possible 

 movement, there is always more or less of interruption in the continuity of the 

 structures which bind the osseous elements together. That is, there is always some 

 evidence of a cavum articulare (joint cavity), although as a matter of course such 

 interruption can never be so extensive as to entirely disassociate the articulating 

 elements. Therefore in all movable joints a new class of structures is found, viz., 

 ligamenta (the ligaments), by means of which continuity is maintained even when 

 all the other uniting media have given place to an articular cavity. The further 

 subdivision of this group is founded upon the amount of movement permissible, and 

 the extent to which the articular cavity takes the place of the original continuous 

 uniting medium. Thus we obtain the amphiarthroses, or partly movable, and the 

 diarthroses, or freely movable. 



An amphiarthrosis (Fig. 292) presents the following characteristics : (a) 

 partial movement ; (6) union by ligaments and by an interposed plate or disc of 

 fibro-cartilage, in the interior of which there is (c) an incomplete or partial joint 

 cavity, which may be lined by a rudimentary stratum synoviale (synovial membrane) 



