ARTICULAR CARTILAGE. 
147 
In birds, the articular cartilage is always more or 
less fibro-cartiiaginous. In the Turkey , the fibres 
proceed in straight lines in the direction of the shaft, 
the cartilage cells being arranged in rows between 
the fasciculi of fibres. The articular surface of the 
specimen Fig. 115, exhibits fibres running in various 
directions among the cartilage-cells ; this arrangement 
is constant in birds, and is precisely similar to that 
occurring in fishes. It is a remarkable fact, that in 
birds there is little or no cartilage except that of the 
FIG. 115 . 
FIG. 116 . 
Articular surface of cartilage of the 
femur of a Turkey. 
Vertical section of articular cartilage 
of the femur of a Turkey. 
articular surfaces of the joints, and occasionally the rings 
of the trachea ; all the parts of the skeleton of these 
animals are rapidly converted into bone, and even 
in the joints, the coating tissue, Fig. 116, often of 
considerable thickness, is composed of fibro-cartilage. 
The moment, however, we examine sections of 
articular cartilages in the Mammalia, we find a 
constant arrangement of the cells, and in the adult 
l 2 
