44-O Anatomy Applied to Medicine and Surgery. 



inches vertically and one and a half inches from side to 

 side. The orbital fat forms a pad for the eyeball and acts 

 as a support for it and for the muscles, nerves and the 

 bloodvessels contained in the cavity of the orbit. The 

 eyeball is composed of the cornea, the sclerotic, the cho- 

 roid and the retina, with the lens, internally, separating 

 the aqueous from the vitreous humor, and having the iris 

 in front of it dividing the space between it and the cornea 

 into two chambers. It, i.e., the eyeball, forms along with 

 the capsule of Tenon, which is' a lymphatic space surround- 

 ing the posterior two-thirds of the eyeball, a ball and soc- 

 ket joint. The orbital fascia receives accessions from the 

 dura mater through the optic canal and the sphenoidal fis- 

 sure and forms a layer for the bones the periorbita. 

 This fascia surrounds the individual muscles, nerves 

 and bloodvessels, and, anteriorly, sends a lamina 

 underneath the eyeball as far as the attached margin 

 of the tarsal cartilage of the lower lid, and this layer of 

 fascia, because of its function, is termed the suspensory 

 ligament of the eyeball. From the sheaths formed by the 

 fascia around the muscles, offsets are sent to the margin 

 of the orbit, and these form check ligaments which prevent 

 displacement from muscular action and limit excessive 

 movement of the eyeball. The nerves of this region are 

 the third, fourth, ophthalmic division of the fifth, sixth 

 and the optic nerve and their relative position in the dif- 

 ferent situations is as follows : In the cavernous sinus, 

 the third, fourth and the ophthalmic division of the fifth 

 lie along the outer wall of the sinus, which is formed by 

 the dura mater, in the order named, both from above 

 downwards, and from within outwards. Along the inner or 

 bony wall of the sinus, is the carotid artery with the sixth 

 nerve on its outer side ; while between them is the venous 

 channel. In the roof of the sphenoidal fissure, the rela- 



