Chap, iv.] THE ORBIT AND EYE. 35 



inner margin of the orbit above the level of the 

 tendo oculi, which may cause displacement of the 

 globe downwards, outwards, and forwards. The bones 

 of the orbit are peculiarly apt to be the seat of ivory 

 exostoses, which may in time entirely occupy the orbital 

 cavity. At the upper and outer angle of the orbit a 

 congenital sebaceous cyst is sometimes met with. It 

 lies beneath the orbicularis muscle, and is often con- 

 nected at some depth with the orbital periosteum. 



According to most French anatomists, the orbit is 

 divided into two distinct spaces by a process of fascia 

 known as the capsule of Tenon. The descriptions, 

 however, of this capsule are still of the most contra- 

 dictory character. Viewed in its simplest aspect, it 

 may be said to be attached all round to the margin of 

 the base of the orbit, at which line of attachment it 

 will be found to be connected with the orbital 

 periosteum. It then passes backwards behind the 

 globe, lying close to the sclerotic, and the fibres, 

 coming from all parts of the orbital margin, meet at 

 last at the optic nerve, with the outer sheath of which 

 the " capsule " is continuous. As thus viewed, this 

 fascia forms a dome for the eye-ball, and shuts it off 

 from the posterior part of the orbital cavity, just as 

 the diaphragm shuts the liver off from the thorax. 

 It has been maintained that the capsule of Tenon has 

 great influence upon the forward progress of orbital 

 abscess ; but this is difficult to understand, since, at 

 its very best, the capsule is but a feeble membrane, 

 lax in its attachments, and very loose in texture. It 

 probably has but a trifling influence upon intra- 

 orbital inflammations. Between the capsule and the 

 sclerotic is a lymph space lined with epithelioid cells, 

 which, with the capsule, forms a kind of socket for 

 the globe in its movements. 



Tenon's capsule is pierced by the ocular muscles, 

 to each of which it gives a process that blends with 



