ARTICULAR CARTILAGE. 
145 
it, these are indicated by the four oval spots or holes, 
two of which are shown as being filled with injection. 
In adult Mammalian articular cartilage, represented 
by Fig. 114, the arrangement of the cells is very 
peculiar ; the cartilage is separated from the bone by 
a white layer (c) of variable thickness, and which 
contains bone-cells three or four times as large as 
those of ordinary bone. This is the non-vascular 
lamella first described by Mr. Toynbee, the lower por- 
tion is connected with the osseous tissue of the shaft 
of the hone (b), while the upper is more or less tuber- 
culated for the attachment of the cartilage. The cells 
in the lowest layer of cartilage, or those immediately 
above the lamella, are arranged in columns parallel 
to the axis of the shaft of the bone, but as we pro- 
ceed to the articular surface, the columns become 
smaller, more numerous, and their direction is changed, 
so that they are now at right angles to the axis of the 
shaft. Immediately on the articular edge of the 
section (a), the cells are so much flattened as to 
present the appearance of epithelium cells, and the 
intercellular substance or matrix of the cartilage, 
assumes a fibrous appearance. Adult articular cartilage 
is not vascular ; the capillaries of the osseous tissue 
of the shaft of the bone terminating in loops as they 
approach the non-vascular lamella. From this brief 
outline of the structure of articular cartilage in the 
young and adult condition, I proceed to notice some 
peculiarities in that of fishes, reptiles, and birds. 
L 
