260 
OBSERVATIONS ON SOUNDNESS. 
which is a fine, elastic, and exquisitely transparent membrane, 
exactly applied to the inner surface of the cornea proper; the 
last is the lining membrane of the anterior chamber of the 
eyeball. The choroid is the vascular membrane of a black, 
soft, and delicate texture, situated immediately under the 
sclerotic, to which it is connected by a very fine, cellular tissue, 
and by the passage of nerves and vessels. Internally it lies 
in simple contact with the retina; it is pierced posteriorly for 
the passage of the optic nerve ; it is connected anteriorly with 
the iris, ciliary processes, and with the line of junction of 
the cornea and sclerotic, by a dense, white line, called the 
ciliary ligament, which surrounds the circumference of the 
iris like a ring. The choroid is formed of three layers—an 
external or venous layer, termed the vencB vorticosae, which 
layer is that connected to the ciliary ligament; secondly, the 
middle ox arterial layer, made up principally of the ramifications 
of minute arteries, which is called the tunica Ruyschiana:* 
the reflections of this layer form the ciliary processes. The 
third and last layer is the pigmentum nigrum ; it is a delicate 
membrane, situated internally; it presents several colours 
spread over the choroid, which are known by the names of 
pigmentum nigrum and iapetum lucidum ; this latter is situated 
above the optic termination. 
The ciliary ligament is the bond of union between the 
external and middle tunics of the eye, and serves to connect 
the cornea and sclerotic at their line of junction with the iris 
and outer layer of the choroid. The canal of Fontana is 
known to exist in this ligament; it is a vascular canal. 
The iris forms the curtain or septum between the anterior 
and posterior chambers; the opening in its centre is termed 
the pupil, the shape of which is horizontally elliptical; the 
margins of the iris are obtruded upon by several small, pen¬ 
dulous bodies, termed the corpora nigra. The front surface of 
the iris points to the cornea, and the posterior towards the 
lens. This muscular arrangement is composed of two layers; 
the anterior one consists of radiating fibres, which converge 
from the circumference towards the centre, and produce an en¬ 
largement of the opening; the posterior or circular surrounds 
the pupil like a sphincter muscle, and produces contraction 
of the pupil. The posterior surface of the iris is of a deep- 
purple tint, thence termed uvea, from its resemblance in colour 
to a ripe grape. 
The ciliary processes consist of a number of triangular 
* “Ruysli was bora at the Hague in 1638 ; his whole life was spent in 
making injected preparations. He discovered this layer, hence the name.”— 
Wilson. 
