Monthly MlcroscoplcaH 
Journal, Nov. 1, 1869. J 
Histology of the Eye. 
237 
In the white rabbit, the muscular bundles of the sphincter 
pupillae are disposed with great regularity in lines concentric with 
the pupil, at the edge of which they form a very distinct band upon 
the anterior surface. On the back of the iris, the outer border of 
the muscular ring is less distinct ; and here, intersecting the radial 
bundles of the dilator, a thin layer of circular fibres is traceable for 
some distance towards the great circumference of the iris. 
The dilator pupillae consists, in this animal, of slender bundles 
running along the posterior surface of the iris from near the great 
circumference towards the pupil, separating and combining again in 
a plexus with long narrow meshes. On nearing the sphincter pu- 
pillae, they spread slightly, and, intersecting with one another and 
with the bundles of the sphincter, are lost. 
The peripheral relations of the radial muscular bundles are less 
easily made out. The difficulty is occasioned by the greater thick- 
ness of the iris, and by the parallel direction of the very muscular 
arteries. I am inchned to think that the bundles attach themselves 
to the elastic fibres, which the ligamentum pectinatum iridis pro- 
longs inwards to the iris. This very remarkable net of elastic 
tissue, which fixes the great circumference of the iris to the margin 
of the anterior chamber, is derived from the posterior elastic lamina 
of the cornea, which in my last lecture I mentioned as having peri- 
pheral relations with the ciliary muscle, iris, and sclerotic. These 
I shall now explain. The lamina at the circumference of the cornea 
resolves itself into fibrous tissue. This dehiscence begins first on 
its anterior surface, and goes on until the whole membrane is con- 
verted into fibres, which take three principal directions. One set 
passes backwards and outwards to the sclerotic, behind the circulus 
venosus in Schlemm's canal ; another set goes directly backwards to 
the ciliary muscle ; and a third set springs across the margin of the 
anterior chamber to the great circumference of the iris, on the ante- 
rior surface of which they form a network remarkable for its hard 
stiff outlines, from which fibres are produced upon the front and in 
the substance of the iris for a considerable distance towards the 
pupil. 
The Uood-vesseh of the iris are very numerous. Its arteries 
come from the arterial circle formed by the inosculation of the two 
long posterior ciliary arteries, and known as the circulus arteriosus 
iridis. The mode of formation of this arterial circle is very vari- 
able ; but the ordinary plan is, that each of the two long posterior 
ciliary arteries divides upon the outer surface of the ciliary muscle, 
near its front, into a couple of primary branches, which separate 
and encircle the iris, and meet the corresponding branches of the 
other long ciliary artery. The arterial circle thus made sends 
branches backwards to the ciliary muscle; others inwards to the 
ciliary processes ; and a third set run forwards to the iris through 
