THE EYE. 



829 



consists, in part, of the larger branches of the short ciliary arteries which run 

 forward between the veins, before they bend inward to terminate in the capillaries ; 

 but is formed principally of veins, which are named, from their arrangement, vena* 

 vorticosa. They converge to four or five equidistant trunks, which pierce the 

 sclerotic midway between the margin of the cornea and the entrance of the optic 

 nerve. Interspersed between the vessels are dark star-shaped pigment-cells, the 

 offsets from which, communicating with similar branchings from neighboring cells, 

 form a delicate network or stroma, which toward the inner surface of the choroid 

 loses its pigmentary character. The internal layer consists of an exceedingly fine 

 capillary plexus, formed by the short ciliary vessels, and is known as the lamina 

 chorio-capillaris or tunica Ruyschiana, The network is close, and finer at the 

 hinder part of the choroid than in front. About half an inch behind the cornea 

 its meshes become larger, and are continuous with those of the ciliary processes. 



FIG. 442. The veins of the choroid. (Enlarged.) 



These two laminae are connected by an intermediate stratum, which is destitute of 

 pigment-cells and consists of fine elastic fibres. On the inner surface of the lamina 

 chorio-capillaris is a very thin, structureless, or, according to Kolliker, faintly 

 fibrous membrane, called the lamina basalis or membrane of Bruch ; it is closely 

 connected with the stroma of the choroid, and separates it from the pigmentary 

 layer of the retina. 



Tapetum. This name is applied to the iridescent appearance which is seen in 

 the outer and posterior part of the choroid of many animals. 



The ciliary body should now be examined. It may be exposed, either by detaching the 

 iris from its connection with the Ciliary muscle, or by making a transverse section of the globe, 

 and examining it from behind. 



The ciliary body comprises the orbiculus ciliaris, the ciliary processes, and the 

 Ciliary muscle. 



The orbiculus ciliaris is a zone of about one-sixth of an inch in width, directly 

 continuous with the anterior part of the choroid ; it presents numerous ridges 

 arranged in a radial manner. 



The ciliary processes are formed by the plaiting and folding inward of the 

 various layers of the choroid i. e., the choroid proper and the lamina basalis at its 

 anterior margin, and are received between corresponding foldings of the suspensory 

 ligament of the lens, thus establishing a connection between the choroid and inner 

 tunic of the eye. They are arranged in a circle, and form a sort of plaited frill 

 behind the iris, round the margin of the lens. They vary between sixty and eighty 

 in number, lie side by side, and may be divided into large and small ; the latter, 

 consisting of about one-third of the entire number, are situated in the spaces 



