JOINTS. 



of syndesmosis in which the serrate borders of bones are connected by 

 short fibrous ligaments. The intervertebral ligaments are synchondroses, 

 each consisting of a fibrocartilage which has at its center a soft mucoid 

 substance containing large groups of cartilage 

 cells. This nucleus pulposus is usually inter- 

 preted as the remains of the notochord, but 

 some consider that the notochord is entirely 

 absorbed, making the nucleus pulposus an 

 independent formation. The term ligament, it 

 will be noted, is applied to bands of various 

 sorts, fibrous, elastic or cartilaginous. 



In a diarthrosis the mesenchymal tissue 

 between the bones remains comparatively loose 

 in texture and a cleft forms in it, containing 

 tissue fluid. This is the joint cavity, Fig. 70. 

 It is bounded by mesenchymal cells which 

 spread out and form an epithelium, shown in 

 Fig. 71. The epithelium may fuse with the articular cartilage so that the 

 latter, uncovered by perichondrium, forms a part of the wall of the joint 



FIG. 70. PHALANGEAL JOINT 



FROM A FOUR MONTHS' 



FETUS. 

 Car., Cartilage; j. c., joint cavity; 



s. f., stratum fibrosum; s. s., 



stratum synoviale. 



FIG. 71. AN ENLARGED DRAWING OP THE LEFT PART OF THE JOINT SHOWN IN FIG. 70. 

 b. v., Blood vessel; car., cartilage; j. c., joint cavity; mes. epi., mesenchymal epithelium. 



cavity. Articular cartilages are usually hyaline layers from 0.2 mm. to 

 5 mm. thick, becoming thin at the periphery. The cells near the joint 

 are flattened parallel \vith the free surface, and some of the deeper of these 



5 



