180 



EYE. 



'On the outside and anterior part of the 

 choroid, where the margin of that membrane 

 corresponds to the place of union between the 

 sclerotic and cornea, a peculiar and distinct 

 formation exists apparently for the purpose of 

 securing a firm union between the two mem- 

 branes. It is commonly called the ciliary liga- 

 ment, also orbiculus ciliaris, circulus ciliaris, 

 by Lieutaud plexus ciliaris, by Zinn annulus 

 cellulosus, and by Sbmmerring gangliform ring. 

 It is a gray circle of soft cellular membrane 

 about two lines broad, applied like a band 

 round the margin of the aperture into which 

 the iris is fitted. It adheres closely to the 

 choroid, and almost equally closely to the scle- 

 rotic, especially in the groove where the cornea 

 joins that membrane. It contains few red 

 vessels, and is not stained by the black pig- 

 ment; consequently it is of a whitish colour. 

 The ciliary nerves penetrate it and subdivide 

 in its structure. Hence it has been considered 

 by Sommerring as a ganglion, and had been 

 previously described by Lieutaud as a nervous 

 plexus. The ciliary nerves, however, merely 

 pass through, and may easily be traced on to 

 the iris. It is evidently a mere band of cellular 

 membrane serving to bind the choroid and 

 sclerotic together at this point, and is obviously 

 a provision essentially necessary for the perfec- 

 tion of the anatomical mechanism of the eye, 

 as without it the aqueous humour must, from 

 pressure on the eyeball, be forced back be- 

 tween the two membranes. In man it is broader 

 in proportion than in the larger quadrupeds, 

 and in birds it is particularly large and dense, 

 adhering more closely to the circle of osseous 

 plates than to the choroid, and consequently 

 presents a very remarkable appearance when 

 the latter membrane is pulled off with the 

 ciliary processes and iris, an appearance to 

 which the attention of anatomists was first 

 drawn by Mr. Crampton. From its position 

 and appearance the ciliary ligament has often 

 been suspected to be a muscular organ, destined 

 by its contraction to alter the form of the cornea, 

 and thus adapt the eye to distance. There is 

 not, however, sufficient evidence to sustain 

 such an opinion. The plate introduced to 

 represent the ciliary nerves, as well as that 

 which represents the iris, exhibit this part of 

 the organization of the eyeball in connexion 

 with the choroid. 



On the inside of the choroid, surrounding 

 the aperture into which the iris is fitted, and 

 corresponding in position within to the ciliary 

 ligament without, exists another peculiar pro- 

 vision destined to establish a connexion between 

 this part and the hyaloid membrane of the 

 vitreous humour, as the ciliary ligament esta- 

 blishes a similar connexion between the sclerotic 

 and choroid. This is the corpus ciliare or 

 ciliary processes, called sometimes incorrectly 

 ciliary ligament, and by Sommerring corona 

 ciliaris. It is composed of a number of dis- 

 tinct folds or productions of the choroid, having 

 their anterior extremities extended to the back 

 of the iris, while the posterior gradually dimi- 

 nish until lost in the membrane from which 

 they originate. Each fold or ciliary process is 



a production or continuation of the choroid, 

 and cannot be separated from it unless clipped 

 off by the scissors. They appear to be com- 

 posed altogether of a remarkable interlacement 

 of arteries and veins derived from those of the 

 choroid, and exhibit no appearance whatsoever 

 of muscular organization, although considered 

 by Porterfield and others as endowed with that 

 function. These are sixty or seventy in num- 

 ber, fifty-seven being enumerated by Sommer- 

 ring, and seventy by Zinn. They are about 

 two lines in length, but are not equally so, 

 every alternate one being shorter than the next 

 to it. The free internal margin of each ciliary 

 process is buried in the hyaloid membrane of 

 the vitreous humour at its anterior part, round 

 the circumference of the crystalline lens, and a 

 corresponding production of the hyaloid mem- 

 brane projects into the space between these 

 processes so as to establish a most perfect bond 

 of union between the two structures. The 

 ciliary processes appear to be attached to the 

 circumference of the lens, and are often de- 

 scribed as having such connexion. This, how- 

 ever, is not the case. The anterior extremities 

 do not touch the circumference of the lens; 

 they project into the posterior chamber of the 

 aqueous humour up to the back of the iris, 

 and consequently constitute the circumferen- 

 tial boundary of that cavity. When the eye 

 becomes flaccid from evaporation after death, 

 the ciliary processes fall down to the margin of 

 the lens and appear to adhere ; but if the cornea 

 and iris be removed from the eye of a subject 

 recently dead, a circle of hyaloid membrane 

 may distinctly be seen occupying the space 

 between the ciliary processes and lens, through 

 which the observer can see to the bottom of 

 the eye. This space is represented and pointed 

 out in Sommerring's plates. The annexed 

 figure from Zinn's work represents the corpus 

 ciliare or circle of ciliary processes on a large 

 scale. 



Fig. 105. 



The choroid, in common with several other 

 parts of the eye and its appendages, is stained 

 by a black colouring matter secreted in and 

 upon different textures. In man it is of a dark- 

 brown colour, but in other animals is generally 



