INTRODUCTORY 



21 



1. Incomplete joints by continuous union, or Synarthro'ses. 



2. Complete joints by discontinuous union, or Diarthro'ses. 



In the Synarthroses 1 the apposing surfaces of the united bones are 

 firmly bound together throughout their whole extent by an interposed 

 tissue, which, after the removal of all the surrounding muscles and 

 ligaments, must be entirely cut through before the bones can be 

 separated. 



In the Diarthroses 2 the apposing surfaces of the united bones are 

 free, and are held in contact by an investing capsule of fibrous tissue, 

 the capsular ligament, the division of which, if the muscles and cer- 

 tain accessory ligaments have been removed, permits the separation 

 of the bones. 



Synarthroses, or incomplete joints, are divided into four classes, 

 namely, the synchondroses, the syndesmoses, the sutures, and the 

 synsarcoses. The classification is based upon the nature and the 

 amount of the uniting tissue : 



1. In a Synchondro'sis 3 the bones are united by a plate of car- 

 tilage. A union of this kind may be movable; for example, a union 



a 



FIG. 7. 



*Cartilage_j 



Suture. 



^.Ligament. 



-Suture. 



DIAGRAM OF A SYNARTHROSIS. 



DIAGRAM ILLUSTRATING DENTATE AND SQUA- 

 MOUS SUTURES. 



of vertebrae by means of cartilaginous intervertebral disks (Fig. 7, a] ; 

 or motion may be so far restricted that the bones practically coalesce by 

 sym'physis ; 4 for example, the two hip-bones are joined by a ventral 

 median symphysis. A similar union, probably without motion, obtains 

 in young, growing bones between the secondary parts, or epiphyses, 

 and the principal part, or diaphysis ; in these cases, however, the 



1 From (Gr.) syn, together, and arthros, a joint. 



2 From (Gr.) dia, between, and arthros, a joint. 



3 From (Gr.) syn, together, and chondros, cartilage. 



4 From (Gr.) syn, together, and phuein, to grow. 



