Monthly Microscopical! Histology of Minute Blood-vessels. 211 
their course certain remarkable forms, which may be compared to 
the Wormian bones of the cranial sutures. These are the so-called 
stomata. They are irregularly rounded in form, and 
vary from the yo}ooth to the zopoth of an inch in 
long diameter. Those shown in the photograph pre- 
sent a clear central space, bounded by a sharp, black 
outline, which is sometimes even thicker than the 
boundaries of the cells themselves. The nuclei of the 
epithelial cells are not shown. The cut exhibits one 
of these cells, a, with portions of the boundaries of 
adjacent cells, b, b, b, and the stomata, ¢, ¢, ¢. 
VI. Sketch of a photograph representing a minute 
artery, with part of the adjoming network of capillaries, 
from the muscular coat of the urinary bladder of the 
frog. Negative No. 220, New Series. From prepara- 
tion No. 8378, Microscopical Section. Magnified 400 
diameters by Wales’s th objective. The field is crossed 
by a small artery, -7ooth of an inch in diameter. Its epithelial 
cells are longer in proportion to their width than those of the veins. 
They average z}oth of an inch in length, and have nuclei similar to 
those of the venous epithelium. Wherever the capillaries come into 
focus the epithelium of their walls is also plainly shown. In the 
intervascular spaces the nuclei of the muscle and connective tissue 
appear as in the first photograph. The cut presents an outline of a 
VOL. IV. : Q 
