390 Royal Society. 



layers according to their affinities, while the whole was subjected to 

 pressure acting along certain axes of elevation, which raised those 

 layers into arches. 



Feb. 26. — The following paper was read : — " On the Motions of the 

 Iris." By B. E. Brodhurst, Esq., M.R.C.S. Communicated by Thomas 

 Bell, Esq., Sec. R.S. 



The observations made in this paper are distributed under three 

 heads. First, the author examines the iris in conjunction with the 

 organic system of nerves. Secondly, he exposes the relation of the 

 several nerves of the orbit in reference to the iris. And, thirdly, by 

 tracing the membrane through the lower orders of animals, he shows 

 the influence of the ophthalmic ganglion upon the iris, and the ne- 

 cessity of its presence for the accomplishment of the motions of the 

 membrane, i. e. contraction and dilatation of the pupil. 



It is shown that the pupil is most contracted during healthy sleep, 

 and especially during that of childhood ; that in death it assumes a 

 median state, neither contracted nor dilated ; and that, when disease 

 is present, the pupil is always dilated, and dilated in accordance 

 with the effect produced upon the trisplanchnic system of nerves. 

 Also, it is stated that the pupil is dilated, when through disease the 

 action of the voluntary muscles is abnormally increased, but that it 

 is contracted when the functions of nutrition are well and actively 

 performed ; and that, with concussion and compression of the brain, 

 the pupil is usually dilated when the power of the voluntary muscles 

 yet remains ; that it is fixed and immoveable when total insensibility 

 exists ; contracted when pressure or counter pressure is made upon 

 the corpora quadrigemina of the opposite side, and dilated when the 

 injury is more general, but less severe. 



The author refers the first class of motions, or the primary mo- 

 tions of the iris, directly to the sympathetic system of nerves; 

 whilst the direct movements, or those produced by the sensation of 

 light, are effected through the cerebral nervous arc, as shown by 

 Flourens, Marshall Hall, and others : and he thinks that contrac- 

 tion of the pupil, when a near object is presented to the eye, may 

 be explained by the greater stimulus thus afforded to the retina and 

 the sensorium ; for he finds that when a near object is presented to 

 the eye with a faint light, but a more distant one with a strong 

 light, the pupil is most contracted for the more distant object. 

 That the influence of the retina and the cerebral nervous arc is 

 secondary in producing the motion of the iris, and that this mem- 

 brane is not a mere diaphragm for the admission or exclusion of 

 light, but that it yields to mental impressions, as well as to those 

 which operate on the vegetative system of nerves, in preference to 

 the effect upon the retina, is shown by the result which is produced 

 upon the iris by any sudden passion in causing dilatation of the 

 pupil, notwithstanding that a strong light be at the same time thrown 

 upon the retina. Hippus, and the motions of the iris which are 

 observed, especially in amaurotic children, are alluded to as motions 

 independent of the light, and consequently, of the retina and sen- 

 sorium. 



