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HISTOLOGY OF ANIMALS. 
In fishes, as in the vertical section of the jaw of 
a Conger eel , the cartilage-cells are small in size, very 
few in number, and arranged without much order in a 
distinctly fibrous matrix, the fibres of which follow the 
direction of the shaft of the bone. Upon the articular 
surface, however, the cartilage-cells are minute, and 
arranged in parallel rows ; but they are so abundant 
as to obscure all trace of fibres. 
In reptiles, as in the Tortoise , the articular or free 
surface of the cartilage has a distinctly fibro-cartilaginous 
structure; the fibres interlace and produce meshes, in 
which the cartilage-cells are lodged. Near the bone the 
fibres disappear, and the cells are of an oval shape, 
and few in number. The most remarkable circumstance 
in connection with this specimen is the great thickness 
of the fibro-cartilage of the articular surface. 
In the Batrachia , as may be observed in a section 
of the head of the femur of a Frog, the cartilaginous 
matrix is clear and transparent ; the cartilage-cells 
are smallest and most numerous in the part nearest 
the bone, but as we proceed towards the articular 
surface they become larger, and the nuclei are more 
plainly seen. The most interesting fact connected 
with the cartilage of the Batrachia is, the large size and 
uniformity of arrangement of the cells upon the arti- 
cular surface ; they are perfectly flat, resemble scales 
of tessellated epithelium, and many of them exhibit 
an appearance of one large cell dividing into four by 
cruciform fissures at right angles to each other. 
