102 EVOLUTION or r nii': IICMAN EYE 



(a) Abnormal deposit of retrobulbar fat. 



(b) Relaxation of rccti muscles from fatty degeneration. 



(c) Serous infiltration of the retrobulbar connective and 

 fatty tissue of the orbit from vasomotor disturbance caused 

 by toxemia from thyroid disturbance. 



(<7) Venous congestion. 



(e) Localized arterial dilation. 



Postmortem examinations have failed to substantiate 

 the presence of any of these conditions. Localized arterial 

 dilation would produce pulsating exophthalmos. Venous 

 orbital congestion would, if it produced proptosis, also pro- 

 duce retinal venous dilation a condition which is never 

 seen. None of these theories will account for the fluctu- 

 ations in the degree of the proptosis in the way in which 

 contraction and relaxation of a muscle tissue will do. 



The effect of the contraction of Miiller's muscle in the 

 human eye, situated as it is in the loose periosteum of the 

 orbit, would be, as in other animals, to press forward the 

 fat of the orbit and consequently the eyeball which lies in 

 front of the fat. Under such circumstances, if, in a case 

 of exophthalmos, an incision was made through the orbito- 

 tarsal ligament, we should expect the fat, being pushed 

 forward and kept in a state of tension, to well up through 

 the incision. We should also expect that in extreme cases 

 of exophthalmos, in which ulceration of the cornea was 

 threatened, recession of the eye and beneficial results might 

 attend removal of some of the fat. Foster Moore 55 has 

 recently recorded how he performed an operation of this 

 description, removing a 'heaped-up tablespoon of fat' ; 

 through an incision which extended the whole length of 

 the lower conjunctiva! fornix. Afterward the lids were 

 easily approximated and sewed together over the front of 

 the eye, so that the eye was preserved. From the result 



