CHAP. VI.] SYNARTIIItODIAL JOINTS. 133 



compatible with the maintenance of the segments in their proper re- 

 lation with each other and also in extent of motion, from that which 

 is so slight as to admit of almost no appreciable change in the po- 

 sition of the parts, to that which allows of the most ample variety 

 of movement between the segments, consistent with the integrity of 

 the articulation. 



It will appear, then, that the most simple kind of articulation is 

 that by which two parts are so united as that only the slightest ap- 

 preciable degree of motion shall exist between them. This consti- 

 tutes the first great division of joints the Sijnarthrosis, where the 

 parts are continuous, i.e., not separated from each other by an inter- 

 vening synovial cavity. Some anatomists consider all synarthrodial 

 joints to be immovable ; which, although not far from the truth, 

 cannot be said to be strictly accurate. Had immobility been the 

 object to be attained, that might have been more effectually accom- 

 plished by the fusion of the extremities of the segments together, as 

 in anchylosis. 



In the second class of joints, motion is enjoyed freely and fully : 

 this class is designated by the term Diarthrosis : the segments are 

 interrupted completely in their continuity ; the extremities of the 

 bones can only be said to be contiguous. 



Synarthrosis. The general characters of the articulations belong- 

 ing to this class are, 1, that they are very limited in their motion, 

 insomuch as to be considered by some as immovable ; 2, that their 

 surfaces are continuous, i. e. } without the intervention of a synovial 

 cavity, but with that of some structure different from bone. The 

 following varieties may be noticed among synarthrodial articula- 

 tions. 



a. Suture. When the margins of two bones exhibit a series 

 of processes and indentations (dovetailing) which are received and 

 receive reciprocally, with a very thin cartilaginous lamina interposed, 

 this is the ordinary kind of suture, sutura vera, of which three kinds 

 are distinguished : sutura dentata, where the processes are long and 

 dentiform, as in the interparietal suture of the human skull ; sutura 

 serrata, when the indentations and processes are small and fine, like 

 the teeth of a saw, as in the suture between the two portions of the 

 frontal bone ; sutura limbosa, when there is along with the deutated 

 margins a degree of bevelling of one, so that one bone rests on the 

 other, as in the occipito- parietal suture. 



When the two bones are in juxta-position by plain but rough sur- 

 faces, the articulation is likewise said to be by suture, and this is the 

 false suture, sutura notha, of which there are two kinds; sutura 



