176 
HISTOLOGY OF ANIMALS. 
spaces between the radii, and 
forming the great mass of 
the body of the vertebra. It 
is to the radii that I would 
particularly direct attention, 
as these are composed of a 
material very like cartilage. 
In a thin section of the same 
vertebra, in which five rays 
may be distinctly seen, each 
is found to be composed of a 
series of thick-walled cartila- 
ginous cells, arranged in linear 
series ; some of the rays, as 
at c, being composed of one 
row ; others, as at «, of three 
rows of cells. On carefully 
examining any one of these 
rows, an aperture of com- 
munication between the cells may be observed, and 
through each of these apertures a delicate tube passes 
from the centre to the circumference. Whether this 
tube be a blood-vessel or an absorbent cannot be easily 
ascertained ; its tubular character, however, is very 
evident. In a longitudinal section of a vertebra of the 
same fish, the radii, represented by d, are divided in 
the direction of their long diameter : they generally 
occur in bundles of three or four, and the apertures 
through which the tubes pass may be observed at 
fig. 137 . 
Sections from a vertebra of the 
Vaagmaer : a , three rows of cells 
from one of the radii ; b, trans- 
verse section of a vertebra; c, 
one row of cells showing the 
tube passing through them ; d, 
vertical section of one of the 
radii. 
