EYfi. 



any intervening membrane, it constitutes an 

 unexpected anomaly in the animal ceconomy. 

 The consequences of inflammation greatly 

 strengthen the conclusion that the cavity is 

 lined by a membrane of the serous character. 

 The slightest injuries or even small ulcers of 

 the cornea are frequently accompanied by effu- 

 sion of purulent matter into the anterior 

 chamber, from the extension of the inflam- 

 mation into that cavity, constituting the hy- 

 popion or onyx of the books ; and the yellow 

 masses which appear on the iris in syphilitic 

 iritis, whether they are abscesses, or as they 

 are called, globules of lymph, are effusions 

 beneath a delicate membrane, as vessels may 

 be seen with a magnifying glass, ramifying 

 over them. In iritis the rapidity with which 

 adhesions are formed between the margin of 

 the pupil and the capsule, proves that these 

 two structures are covered by a membrane of 

 this nature. In addition to all these facts the 

 still more conclusive one is to be adduced, 

 namely, that the membrane can without diffi- 

 culty be demonstrated on 

 the back of the iris, as 

 I have stated in speaking 

 of that part of the organ, 

 and as it is represented 

 in fig. 127, where the 

 fold of membrane stained 

 with black pigment is seen 

 turned down from that 

 structure. 



In the preceding pages I have availed my- 

 self of whatever valuable and appropriate facts 

 in comparative anatomy I found calculated to 

 illustrate or explain the structure of the human 

 eye. There are, however, two organs in other 

 animals which do not exist even in the most 

 imperfect or rudimental state in the human 

 subject the pecten or marsupium nigrum in 

 birds, and the choroid gland or choroid muscle 

 in fishes. 



Of the pecten. This organ is called pecten 



from its folded form bearing some resemblance 

 to a comb, and mai^supium nigrum from its 

 resemblance in the eye of the ostrich to a black 

 purse, according to the anatomists of the 

 French Academy, who compiled the collection 

 of memoirs on comparative anatomy. The 

 organ is obviously a screen projected from 

 the bottom of the eye forward toward the crys- 

 talline lens, and, consequently, received into 

 a corresponding notch or wedge-shaped hollow 

 in the vitreous humour; it appears to be of 

 the same vascular structure as the choroid, and 

 is deeply stained with the black pigment, 

 which renders it perfectly opaque and imper- 

 vious to light. The annexed figure, from the 

 work of D. W. Sommerring, represents it in 

 the eye of the golden eagle. 



Fig. 128. 



Fig 127. 



It is composed of a delicate membrane, highly 

 vascular, folded exactly like the plaits of a fan, 

 and when removed with sharp scissors from 

 the bottom of the eye, and its free margin cut 

 along the edge so as to allow the folds to be 

 pulled open, it may be spread out into a strip 

 of continuous riband-shaped membrane, as 

 seen in Jig. 129, from a paper of Sir E. 

 Home's in the Philosophical Transactions for 

 1822. 



Fig. 129. 



The first account I find of it is by Petit in 

 the Mm. de I'Acad. Roy. 1735. He says it 

 is a trapezium or trapezoid, five lines long at 

 the base, and three lines and a half deep, com- 

 posed of parallel fibres, and that a fine trans- 

 parent filament runs from the anterior superior 

 an^le to the capsule of the crystalline lens, 

 not easily seen on account of its transparency, 

 and that sometimes the angle itself is attached 

 to the capsule near its margin. Haller, in his 

 work " Sur la formation du cceur dans le 



poulet," describes it as follows: " It is a 

 black membrane folded at very acute angles, as 

 the paper of a fan, upon which transparent 

 vessels are expanded; it generally resembles 

 the ciliary processes. It originates from the 

 sclerotic in the posterior part of the eye by a 

 serrated line, pierces the choroid, retina, and 

 vitreous humour to attach itself to the side of 

 the capsule of the crystalline, very near the 

 corona ciliaris. The posterior extremity is 

 broad, and the anterior narrows till it becomes 



