60 SURGICAL APPLIED ANATOMY. [Chap. iv. 



dura mater, and an inner from the arachnoid. These 

 sheaths remain distinct and separate, and the two 

 spaces enclosed may be injected, the outer from the 

 subdural, the inner from the subarachnoid space. Thus 

 inflammatory affections of the cerebral meninges can 

 readily extend along the optic nerve to the optic disc 

 through these spaces in the nerve sheath, while in 

 cases of intracranial disease other than meningeal, the 

 mischief may extend from the brain to the disc along 

 the interstitial connective tissue in the nerve. These 

 connections may serve in part to explain the frequent 

 association of optic neuritis with intracranial disease. 

 Optic neuritis nearly always implies that the optic 

 disc or papilla is inflamed, but in exceptional cases the 

 changes are limited to that part of the nerve behind 

 the globe (refcro-bulbar neuritis). The entire length of 

 the optic nerve within the orbit is 28 mm. to 29 mm. 

 The aqueous and vitreous humour*. 

 The aqueous fills the space between the capsule and 

 suspensory ligament of the lens and the cornea. The 

 iris divides this space into two parts, the anterior 

 and posterior chambers. Since, however, the iris is 

 largely in actual contact with the lens, it happens 

 that the posterior chamber is represented by a little 

 angular interval between the iris, the ciliary processes, 

 and the zonula of the lens (Fig. 10). The depth of 

 the anterior chamber is 3*6 mm. The cornea at its 

 circumference breaks up into bundles of fibres, which 

 are partly continued into the front of the iris, and 

 which constitute the ligamentum pectinatum iridis. 

 Between the processes of this ligament there are 

 intervals which lead into certain cavernous spaces 

 called the spaces of Fontana. These spaces in their 

 turn communicate with a large circular canal situate 

 in the sclerotic close to its junction with the cornea, 

 and known as the canal of Schlemm. This space ig 

 in communication with the veins of the anterior part 



