54 DR KNOX on the Comparative Anatomy of the Eye. 



tions, that the annulus albus assumed a variety of appearances, 

 but that it resembled a ligament in a very few animals only : 

 that in still fewer did it bear any resemblance to a nervous 

 ganglion ; which resemblance, I speedily satisfied myself, was a 

 complete deception. At last, having discovered, that in birds, and 

 in the deer, the so named ligament received numerous nerves, 

 that its texture bore no resemblance whatever to ligament, that 

 it became rudimentary in those animals whose sight was feeble, 

 which would not necessarily happen were it simply a ligament 

 for the suspension of the tunics and humours of the eye ; the 

 conclusion was irresistible ; that the annulus albus is a muscle, 

 that it is the muscle by which the eye adapts itself to the percep- 

 tion of distant objects, and that by it, in conjunction with the 

 iris, all the changes which take place in the interior of the eye- 

 ball are effected *. 



In compliance with the wish of some of my friends, small 

 sections of the annulus albus were submitted to the microscope. 

 The result of this investigation was, that it had no resemblance 

 to a ligament ; that it contained comparatively large branches of 

 nerves ; that it did not resemble any of the textures of the eye- 

 ball except the iris, but that here the resemblance was so close 

 that they could with difficulty be distinguished. 



It were desirable that I should bring forward ample collate- 

 ral proofs of the presence of this great central muscle of the 

 eye-ball, and which I shall henceforward call the Ciliary Muscle; 

 but I am by no means prepared for so extended an inquiry : 

 many, however, will readily suggest themselves to those who 

 have investigated the eye anatomically in a variety of animals. 

 Birds, for example, that have a strong ciliary muscle, amply sup- 

 plied with nerves, have powerful vision ; their perception of ob- 



* The opinion that the annulus albus is muscular, has been often maintained, but, 

 so tar as I know, no proofs, derived from anatomy, of its muscularity, have ever been 

 laid before the public. 



