Chap, iv.] THE ORBIT AND EYE. 59 



with its capsule, is in all parts perfectly transparent 

 and perfectly non-vascular. The lens may easily be 

 loosened or displaced by partial rupture of its 

 suspensory ligament, and may find its way into the 

 anterior chamber, or, more commonly, back into the 

 vitreous. The lens, if disturbed, may swell, and by 

 the pressure thus exercised cause great damage to the 

 important structures adjacent to it. The capsule is 

 very brittle and elastic, and when torn its edges curl 

 outwards. It has to be lacerated in all cataract opera- 

 tions, and may be ruptured by many forms of violence 

 applied to the eye-ball. When the capsule is wounded 

 the aqueous humoiir enters, and is imbibed by the 

 lens fibres, which in consequence swell up, and become 

 opaque, thus producing a traumatic cataract. In the 

 various forms of cataract the whole lens, or, more 

 commonly, some portion of it, becomes the seat of 

 opacity. This often commences in the nucleus, and 

 for a long while remains limited to that part ; or it 

 may first involve the cortex, and in such a case the 

 opacity takes the form of a series of streaks that point 

 towards the axis of the lens, and are dependent upon 

 the arrangement of the lens fibres. " In so-called 

 ' concussion cataract,' where after a blow on the eye a 

 part of the lens becomes opaque, it appears probable 

 that the capsule has been very sHghtly torn opposite 

 to the opacity " (Lawford). 



Of the retina it is only necessary to observe that 

 its connection with the choroid is so slight that it 

 may easily be detached from that membrane by 

 hfemorrhagic, or other effusions, and may indeed be so 

 detached by a simple blow upon the globe. Even 

 when extensively detached it remains, however, as 

 a rule, attached at both the optic disc and the ora 

 serrata. The optic nerve as it passes from the brain 

 receives its perineural sheath from the pia mater, and, 

 in addition, two other sheaths ; an outer from the 



