138 
HISTOLOGY OF ANIMALS. 
FIG. 110 . 
being arranged in the form of radii. Some parts of 
this Chorda dorsalis, especially those near the centre, 
are soft and pulpy ; in these, 
the cells can be separated 
from each other, hut, nearer 
the circumference, the cells 
are more compressed and 
very firmly adherent. 
These large cells are not 
confined to the Chorda dor- 
salis of cartilaginous fishes, 
they exist also in the embryos 
of osseous fishes, and in the 
Tadpoles of batrachians. A 
portion of the vertebral co- 
lumn of a Trout three weeks 
old is represented in Fig. 110; 
the larger cells seen at B con- 
stitute the true Chorda dor- 
salis, which never becomes 
ossified; but above them, as 
at A, a rudimentary neural spine is seen, this is com- 
posed of cells of much smaller size, and characteristic of 
cartilage that is afterwards converted into bone. At 
this early stage, then, we can distinguish between per- 
manent and transitional cartilage. 
In the examples I have hitherto given, no other sub- 
stance than the cells has been alluded to ; the majority of 
cartilages, however, will be found to consist of a matrix 
Portion of the vertebral co- 
lumn of a Trout three weeks 
old : a, part of a spine composed 
of transitional cartilage, b, Chor- 
da dorsalis . 
