PROTECTIVE MECHANISMS OF THE EYEBALL 101 



which may be regarded as the analogue of the 'protrusio 

 bulbi muscle" in lower animals, and which is supplied by 

 the cervical sympathetic nerve, is of considerable clinical 

 interest. 



First, because it has been noted that slight protrusion of 

 the eyeball, or exophthalmos, may occur from stimulation 

 of the cervical sympathetic, and slight recession or enoph- 

 thalmos from its paralysis. Secondly, because overaction 

 of this muscle offers the most satisfactory explanation of 

 the exophthalmos which occurs in connection with Graves' 

 disease. As stated by Andre Crotti 54 the exophthalmos 

 in this affection generally develops slowly, but may come 

 on rapidly. It is liable to fluctuations varying with the 

 physical and mental condition of the patient. It may 

 subside entirely after operation, on the same day as the 

 operation, to reappear again a few days later. It also 

 disappears after death. All these circumstances are con- 

 sistent with the contraction or relaxation of a muscle which 

 has the power of pushing forward the globe. The amount 

 of protrusion which its contraction produces would naturally 

 vary with the state of its development; like other muscles 

 it would tend to hypertrophy and increase in power by pro- 

 longed stimulation. By such increase in its power the 

 increase in the amount of the exophthalmos might be 

 accounted for in the cases of long standing. 



Another symptom of the disease, viz., retraction of the 

 upper lid, is due to contraction of muscle fibers supplied 

 by the cervical sympathetic nerve. This muscle, which 

 was also first described by Miiller, is also named after him, 

 and, like the muscle about the sphenomaxillary fissure, is 

 composed of unstriated fibers. 



A number of other theories have been suggested to account 

 for the exophthalmos in this disease, which may be sum- 

 marized as follows: 



