134 LOCOMOTION. [CHAP. vi. 



squamosa, where the bevelled edge of one bone overlaps and rests 

 upon the other, as in the temporo-parietal suture, and harmonia 

 (ap(o, adapto), where there is a simple apposition : this last kind of 

 articulation is met with, as Bichat observes, wherever the mecha- 

 nism of the parts is alone sufficient to maintain them in their proper 

 situation, as may be seen in the union of most of the bones of the 

 face. 



The sutures have a considerable tendency to become obliterated by 

 age, the intervening cartilage becoming ossified ; it rarely happens 

 that the sutures are all manifest in a human skull past fifty years of 

 age, and sometimes the obliteration takes place at a much earlier 

 period. The frontal suture is by no means permanent ; it is not 

 often found at puberty. In birds and fishes this tendency to the 

 obliteration of the sutures is particularly manifest. 



b. Schindylesis (o-^vSv\rjcr^ } fissio ; <r^&>, diffindo). This form 

 of articulation is where a thin plate of bone is received into a space 

 or cleft formed by the separation of two laminae of another, as is 

 seen in the insertion of the azygos process of the sphenoid bone into 

 the fissure on the superior margin of the vomer ; and in the articu- 

 lation of the lachrymal bone with the ascending process of the 

 superior maxillary. 



c. Gomphosis (70/^09, claws. Clavatio, conclavatio) . When a 

 bone is inserted into a cavity in another, as a nail is driven into a 

 board, or as a tree is inserted into the earth by its roots, the articu- 

 lation is by gomphosis. The only example we have of it in the 

 human subject, or in quadrupeds, is in the insertion of the teeth into 

 the alveoli. 



d. Amphiarthrosis. This is a form of articulation where two 

 plane, or mutually adapted surfaces are held together by a carti- 

 laginous or fibro-cartilaginous lamina of considerable thickness, as 

 well as by external ligaments. In virtue of the elasticity of the in- 

 terposed cartilaginous or fibro-cartilaginous lamina, the amphiar- 

 throsis possesses a manifest, although certainly a very limited degree 

 of motion, and hence most systematic writers class it with the diar- 

 throdial articulations. But it appears much more consistent to place 

 it among the synarthrodial joints, for, 1, its anatomical characters 

 agree precisely with those of synarthrosis ; 2, the surfaces in amphi- 

 arthrosis being continuous, it would make an exception in diarthrosis 

 were we to place it there ; and, 3, its degree of motion is greater 

 than that of suture, only because of the greater development of the 

 interosseous substance. 



The examples of this form of joint in the human body are, the 





