184 



EYE. 



considers it destitute of sensibility, and as- 

 sumes that the pupil is dilated after death. 

 Any anatomist may, however, demonstrate the 

 orbicular muscle ; any surgeon breaking up a 

 cataract, may elicit the irritability, and see the 

 pupil contract, as the fragments of the lens or 

 the side of the needle touch its margin. The 

 pain produced by pinching or cutting the iris 

 in operations for cataract and artificial pupil is 

 no longer matter of doubt, and the assumption 

 that the pupil dilates when death takes place 

 is disproved by daily observation. The pupil 

 contracts to exclude light when too abundant, 

 and dilates to admit it when deficient in quan- 

 tity ; the heart contracts to expel the blood, 

 and dilates to receive it; the diaphragm con- 

 tracts to fill the lungs, and relaxes to assist in 

 emptying them. I can see no material differ- 

 ence between the phenomena exhibited by the 

 actions of the iris, and those displayed by the 

 muscular system generally. I believe that when 

 the pupil contracts to intercept light, that con- 

 traction is accomplished by the orbicular mus- 

 cle, which operates as any other sphincter; 

 and that when the pupil is dilated to admit 

 light, the dilatation is accomplished by the con- 

 traction of the structure, which I have said re- 

 sembles the curnete columns and cordte tendinece 

 in the heart. 



During foetal life the aperture in the centre is 

 closed by a membrane, hence technically called 

 membrana pupillaris. The discovery of this 

 membrane was first announced by Wachendorf, 

 but was subsequently claimed by Albinus, and 

 still later by Dr. Hunter for a person of the 

 name of Sandys. It is usually described as 

 existing from the earliest period of foetal life to 

 the seventh month, when it disappears. In the 

 paper communicated by me to the Medico- 

 Chirurgical Society, I have endeavoured to 

 shew that this description is not correct, but that 

 this membrane continues to the ninth month. 

 The account there given is as follows : " If the 

 eye be examined about the fifth month, the 

 membrana pupillaris is found in great perfec- 

 tion, extended across a very large pupil ; the 

 vessels presenting that singular looped arrange- 

 ment, (with a small irregular transparent por- 

 tion in the centre,) well depicted by Wrisberg, 

 Blumenbach, Albinus, Siimmerring, Cloquet, 

 and others. About the sixth month it is equally 

 perfect; the pupil is however smaller, the iris 

 being more developed. Subsequently to this 

 date the vessels begin to diminish in size and 

 number, and a larger transparent portion occu- 

 pies the centre. At the approach of the eighth 

 month, a few vessels cross the pupil, or ramify 

 through the membrane at a short distance from 

 the margin, without at all presenting the looped 

 ;ip|:r; nance of the previous period, but ad- 

 mitting u free communication between the ves- 

 sels of the opposite side of the iris. The pupil 

 is now still more diminished in size, and the 

 nix has assumed its characteristic coloured ap- 

 pearance; notwithstanding the absence of ves- 

 sels, the membrane still preserves its integritv, 

 though perfectly transparent. The period now 

 appioaclies when it is to disappear; this occur- 

 rence takes place, according to my observations, 



a short time previous or subsequent to birth. 

 In every instance where I have made the exa- 

 mination, I have found the membranu pupillaris 

 existing in a greater or less degree of perfection 

 in the new-born infant; frequently perfect 

 without the smallest breach, sometimes pre- 

 senting ragged apertures in several places, and, 

 in other instances, nothing existing but a rem- 

 nant hanging across the pupil like a cobweb. 

 I have even succeeded in injecting a single ves- 

 sel in the membrana pupillaris of the ninth 

 month. Where I have examined it in subjects 

 who have lived for a week or fortnight after 

 birth, as proved by the umbilicus being healed, 

 I have uniformly found a few shreds still re- 

 maining. It is obvious from the preceding 

 observations, that the membrane does not dis- 

 appear by a rent taking place in the centre, 

 and retraction of the vessels to the iris, as sup- 

 posed by Blumenbach, but that it at first loses 

 its vascularity, then becomes exceedingly thin 

 and delicate, and is finally absorbed. The de- 

 monstration of what I have advanced respect- 

 ing this delicate part is attended with much 

 difficulty, and requires great patience. The 

 display of the membrana pupillaris of the seventh 

 month is comparatively easy ; but at the ninth 

 month, or subsequently, it can only be accom- 

 plished by particular management. The eye, 

 together with the appendages, should be care- 

 fully removed from the head ; it should then 

 be freed from all extraneous parts by the scis- 

 sors, under water, and a careful section made 

 at a short distance behind the cornea; taking 

 care to include the vitreous humour in the divi- 

 sion, in order that the lens may remain in its 

 proper situation. The portion to be examined 

 should now be removed into a shallow vessel of 

 water, to the bottom of which a piece of wax 

 has been secured. The operator should be 

 provided with fine dissecting forceps and nee- 

 dles in light handles; with one needle he 

 should pin the sclerotic down to the wax, and 

 with the other raise the lens, and portion of 

 vitreous humour attached to it, from the ciliary 

 processes, and separate the ciliary ligament 

 from the sclerotic. He may now expect to dis- 

 cover the membrana pupillaris, but its perfect 

 transparency renders it completely invisible; 

 he may, however, ascertain the existence, by 

 taking a minute particle of the retina and 

 dropping it into the centre of the pupil, where 

 it remains suspended if this membrane exist. 

 The preparation should now be taken up in 

 a watch-glass, and placed in a weak mix- 

 ture of spirit and water, and a little pow- 

 dered alum raised on the point of a needle 

 dropped upon it. After a day or two it may 

 be examined ; and if the membrane be pre- 

 sent, it has become sufficiently opaque to 

 be visible, and may now be suspended in a 

 bottle of very dilute spirit." In the annexed 

 engravings, A represents the membrana pu- 

 pillaris of about the fifth month, present- 

 ing the peculiar looped arrangement of the 

 vessels. JB represents the membrane about the 

 eighth month, not presenting the looped ar- 

 rangement. C represents the membrane with a 

 red vessel in its structure at the ninth month. D 



