chap, iv.] THE ORBIT AND EYE. 51 



an inch from the cornea. When the globe is ruptured 

 by violence it is the sclerotic that most commonly 

 yields, the rent being most usually a little way from 

 the cornea, i.e. in or about the thinnest part of the 

 tuiiic. A rupture of the cornea alone from violence 

 is not common. The sclerotic may be ruptured while 

 the lax conjunctiva over it remains untorn. In such 

 a case the lens may escape through the rent in the 

 sclerotic, and be found under the conjunctiva. At 

 the point of penetration of the optic nerve the sclerotic 

 is thin, and pierced by numerous holes for the passage 

 of nerve bundles. This weakened part, the lamina 

 cribrosa, plays an important part in glaucoma (page 

 63). It gives the stippled appearance to the optic 

 papilla. Brailey states that the lateral parts of the 

 sclerotic are thinner than the upper and lower 

 segments, the inferior part being the thickest and 

 the external wall the thinnest. It happens, therefore, 

 that under the influence of intraocular pressure the 

 eye expands more laterally than in the vertical direc- 

 tion. It is mainly to the denseness and unyielding 

 character of the sclerotic that must be ascribed the 

 severe pain (due to pressure on nerves) experienced 

 in those eye affections associated with increased intra- 

 ocular tension (glaucoma, etc.). The choroid is the 

 vascular tunic of the globe, and carries its main blood- 

 vessels. Between the choroid and sclerotic are two 

 thin membranes, the lamina suprachoroidea and lamina 

 fusca, which are separated from one another by a 

 lymph space. In injuries to the globe, therefore, ex- 

 tensive bleeding may take place between these two 

 coats, and indeed a like haemorrhage may be the result 

 simply of a sudden diminution in the ocular tension 

 produced by such an operation as iridectomy or cata- 

 ract extraction. The choroid alone has been ruptured 

 (usually at its posterior part) as the result of a blow 

 upon the front of the eye. The choroid is one of the 



