‘Journal, Ueki Crystalline Lens in Man. 225 
mainly ministers to the nutrition of the retina. It gives, however, 
in its course small twigs for the nutrition of the nerve behind the 
eye-ball, and these reinforced by others derived from minute name- 
less arteries distributed to the sheath, ramify in the septa between 
the nerve-bundles. 
The veinlets accompanying the primary branches of the arteria 
centralis in the retina do not usually coalesce in a single trunk in 
front of the lamina cribrosa; but they pierce this separately and 
first unite the trunk of the nerve behind it. 
In the arrangement of its sheath the optic nerve differs from 
all the other large nerve-trunks. These have but one tightly- 
fitting tube of connective tissue—the external neurilemma; but 
the optic nerve has a double sheath. It has a thin tightly-fitting 
sheath representing that of the nerves, from the inner surface of 
which septa are produced inwards, between the uerve-bundles 
constituting the internal neurilemma or frame which holds the 
bundles together and carries the nutrient blood-vessels. In front 
of the lamina cribrosa, in the nerve-disc, the neurilemma is of the 
very delicate kind to which Virchow has given the name neuroglia. 
Its fibres have two principal directions ; one transverse to that of 
the nerye-bundles, and therefore parallel to those of the lamina 
cribrosa, the other direction vertical to the front of the lamina and 
free surface of the nerve-disc. ‘These last fibres correspond to the 
radial connective-tissue fibres in the retina. The inner sheath and 
internal neurilemma consist of common connective tissue—fibrillated 
bundles with interspersed corpuscles. In front this division of 
the sheath blends with the lamina cribrosa and with the inner 
third of the sclerotic. The outer division of the sheath is con- 
tinuous posteriorly with the dura mater, so that coloured fluids 
injected into the space between the sheaths soon find their way 
backwards into the cranial cavity. In front, this sheath blends 
with the posterior two-thirds of the sclerotic. 
The inner and outer sheaths are loosely connected by a very open 
areolated tissue, composed chiefly of curling fibres and of coarser 
bundles of connective tissue, in which are imbedded large nucleated 
fusiform corpuscles. These give to the interstitial or areolar spaces 
the appearance of an epithelial lming. They play an important 
role in neuritis and in the evolution of morbid growths. 
The space between the sheaths has lately been described as a 
lymph-space. In severe injuries of the head blood is sometimes 
poured out into it. 
