130 
HISTOLOGY OF ANIMALS. 
noticed that cells of the shape represented by c c, are 
very abundant. 
A peculiar form of areolar tissue is found surrounding 
the vessels at the base of the brain of the human subject 
and some of the lower animals ; when acted on bv 
acetic acid, the white fibres, which are arranged in 
separate bundles, assume a tubular form, and the yellow 
element is seen surrounding them, either in the form of 
rings or spiral bands, a circumstance which has led 
some anatomists to suppose that these are blood-vessels 
in an early stage of formation. A specimen of this 
peculiar arrangement from the vessels at the base of the 
brain of a Sheep is represented by e in Fig. 105. 
I now proceed to describe the mode in which simple 
membrane and fibrous tissues are supplied with blood- 
vessels, and the first example I shall take is that of 
the posterior layer of the capsule of the lens, which has 
already been described as a structureless membrane, 
nevertheless, it gives support to large blood-vessels 
derived from the arteria centralis retina, which pass 
forward over the capsule as far as the iris, where they 
divide into two branches. These vessels can be readily 
injected in any young animal, hut in the adult I have 
never yet succeeded in filling them, except in the case 
of certain reptiles, as for example, the Frog , Toad , Newt , 
Common English Snake, and Tiger Boa. In none of 
these animals do the vessels pass farther forwards than 
what may be termed the equator of the lens ; they there 
