24 INNERVATION. [CHAP. XVII. 



The description of the choroid now given refers only to that por- 

 tion of it which corresponds to the retina, and this latter membrane 

 ceases at aline (ora serrata) about an eighth of an inch behind 

 the margin of the cornea. In front of this line, and as far as the 

 iris, the choroid is known as the ciliary body, being modified to 

 form the ciliary process; and it is covered on its outer surface 

 by a semi-transparent tissue, the ciliary muscle, at the anterior edge 

 of which is a more opaque white ring, the ciliary ligament. 



The ciliary processes of the choroid project as folds, or plaitings, 

 into the vitreous humor, and are there lodged in corresponding 

 folds, the ciliary processes of the vitreous body. They are seen from 

 within to commence at the anterior border of the retina, or ora 

 serrata } as mere streaks, converging towards the lens; and it is only 

 when advanced more than halfway to that body that they become 

 projected into about sixty or seventy plaits, with subordinate ones 

 between. These terminate by small free extremities, which 

 slightly overlap in front the border of the lens, without touching it, 

 being united to it through the medium of a delicate layer of the 

 hyaloid membrane of the vitreous humor. These folds take firm 

 hold of the vitreous humor in its front part, all round the lens. 

 Their texture is very vascular (fig. 113, b) and filled with irregular 

 pigment-cells, (which in the human eye are least numerous on the 

 most prominent parts,) and on their inner surface is a tough colour- 

 less lamina, composed of ill-defined nucleated cells, continuous with 

 the border of the retina, but clearly not composed of nervous 

 matter,) by means of which they are immediately connected with 

 the hyaloid membrane. The strength of this connexion is evinced 

 in attempts to sever it in the recent eye. After a certain amount 

 of decomposition has taken place, the separation is much more 

 easy. The ciliary processes by their anterior surface, near their apex, 

 contribute to form the posterior wall and side of the posterior 

 chamber, and are continuous with the back of the iris. They 

 are there free, and washed by the aqueous humor. The ciliary 

 processes are covered, and therefore concealed, on the outside by 

 the ciliary muscle. 



The iris may rightly be regarded as a process of the choroid; it 

 is continuous with it, although of a modified structure. It forms 

 a vertical curtain stretched in the aqueous humor before the lens, 

 and perforated for the transmission of light. It is attached all round 

 at the junction of the sclerotic and the cornea, so near indeed to the 

 latter that its anterior surface becomes continuous in the following 

 manner with the posterior elastic lamina. This lamina near its 



