140 
HISTOLOGY OF ANIMALS. 
have occasion to revert in a future Lecture In car- 
tilaginous fishes generally, all parts of the skeleton, 
except the Chorda dorsalis , are composed of a firm 
hyaline intercellular substance, in which, numerous oval 
nucleated cells are imbedded, they are generally arranged 
in groups of five or six ; distinctly nucleated cells exist 
in the cartilage of the head of a Ray , which also occur 
in fasciculi or groups imbedded in a slightly granular 
matrix. In another section of the cartilage from the 
same Ray, the granular appearance is more evident; 
this portion of the cartilage, which will be alluded 
to hereafter, is undergoing the process of ossification, 
and the granules are those of osseous matter. 
In Reptiles , the cartilage-cells are larger than in 
Fishes , and in the Siren they attain their greatest size ; 
they are smallest in the Crocodilia. In Birds there is 
scarcely any cartilage, except that entering into the 
formation of the joints ; in these animals all the 
cartilage is converted into bone, at a very early period 
of life. 
In the Mammalia we have large cells, and a firm 
structureless intercellular substance ; the largest cells, 
according to my own observations, being those in the 
Elephant. In some cases, the intercellular substance 
is of a fibrous character ; if thin sections be taken 
from the cartilage of the ear of the Rabbit or Dog , the 
cells can be detached from the meshes formed by the 
fibres. In a vertical section of the cartilage of the 
auricle of the human ear, the cells are in some parts 
