238 
Histology of the Eye. 
[Monthly Microscopical 
Journal, Nov. 1, 1869. 
the ligamentum pectinatum. These latter have, as Leber notices, 
very thick muscular walls. They run from the great circumference 
of the iris towards the pupil with a straight or wavy course, detach- 
ing branches to the capillary net, which is very abundant, especially 
at the anterior surface of the iris. On reaching the lesser circle of 
the iris (the httle circlet of minute irregularities on the front of the 
iris near the pupil, which marks the attachment of the foetal pupil- 
lary membrane), the now greatly diminished arteries join here in a 
second arterial ring, the circulus arteriosus minor iridis. From 
the inner border of this, capillaries extend inward, encroaching 
slightly upon the sphincter, but not quite reaching the edge of the 
pupil. 
The veins of the iris lie nearer its posterior than its anterior 
surface. They pass backwards, and, joining the veinlets of the 
ciliary processes, convey the venous blood from the iris to the vasa 
vorticosa. 
The iris receives its nerves horn the ciliary plexus — that exqui- 
site net on the outer surface of the ciliary muscle. I can strongly 
recommend osmic acid for their microscopical demonstration. If 
the iris be placed in a solution of this acid holding about one-fourth 
to one-half a grain per cent, for about twenty-four hours, we get the 
nerves blackened, and the muscular tissue only slightly stained. 
Stronger solutions are not so useful as the weak ones, because they 
blacken more, and less discriminatingly; and, if the preparations 
are left a little too long in them, everything is black alike, and 
indistinguishable. (Fig. 8.) 
The nerves of the iris, most easily studied in white rabbits and 
guinea-pigs, are numerous. The larger bundles, containing several 
fibres, converge from the great circumference of the iris towards 
the lesser circle, forming, in their hitherward course, an open 
plexus, the larger meshes of which are occupied by a finer net. At 
the lesser circle, the nerves combine in a circular plexus, from which 
single fibres are traceable inwards in the sphincter nearly to the 
edge of the pupil. The coarser bundles have a very abundantly 
nucleated neurilemma. The nerve-tubules vary greatly in size, 
ranging between ^-^W' and to^o o". such tubules have a medulla ; 
they are dark-edged fibres ; while the smallest pale fibres which I 
have traced were not more than yro^oo" iii diameter. 
The interstices between the muscular bundles and the meshes of 
the vascular and nervous nets are filled with a homogeneous con- 
nective substance, in which simple, jagged, and very large, irregular, 
and much branched connective-tissue corpuscles, plentifully occur. 
Many of these contain a granular pigment, which, by its quantity 
and distribution, produces the different colours of the iris. 
The back of the iris is overlaid with a coat of pavement-epithe- 
lium, loaded with granular pigment, which is sometimes called the 
