CARTILAGE. 
137 
diameter. At the edges of the ear, the cells are in a 
single layer, but in the thicker parts two or more layers 
are superimposed. In these situations the cartilage is 
precisely similar to certain forms of vegetable cellular 
tissue. 
The ear of the common Mouse may be taken as a 
good specimen of simple cartilage; the central portion 
consists of a series of hexagonal cells arranged in layers 
one over the other, so that in every other respect, 
except in the size of the cells, the structure resembles 
that of a transverse section of the pith of a plant; this, 
however, has been before alluded to, and represented 
in Fig. 99. 
In the thin cartilage of the ear of the Bat above 
named, the cartilage cells are of smaller size, and 
have thicker walls than those of the Mouse ; in all 
parts, especially on the edges, the cartilage is sufficiently 
transparent to be seen through ; and, in nearly every cell, 
as central nucleus may be observed. This, like the pre- 
ceding, has been before de- 
scribed, and is represented in 
Fig. 100. 
The transverse section of 
the Chorda dorsalis of a 
Lamprey , a portion of which 
is represented in Fig. 109, 
consists entirely of large cells 
m , of a more or less hexagonal 
Transverse section ot the Chorda ° 
dorsalis of a Lamprey. figure, those near the margins 
FIG. 109 . 
