Fig. 42. Orbit and surronding Structures — Horizontal Section. 



Front a frozen section which passes horizontally through the middle of the eye 

 of a male body, 4^ years old, the brain is removed; middle Meningeal Artery 

 and Gasserian Ganglion dissected. Mucous membrane of Nasal and Accessory 

 Cavities, red. Tenon's Capsule and Periostenni blue. Lachrymal apparatus 



orange. 



This section shews the conical shape of the orbital cavity which has also 

 been compared with a pyramid. The inner wall is chiefly formed by the Os 

 Planum of the Ethmoid ; it is very thin, and separates the orbit from the accessory 

 nasal cavities. Pus may thus easily spread from them into the orbit. The centre 

 of the eyeball does not lie in the axis of the orbit, but slightly external to it. 

 The orbit is filled with fat through which the muscles, vessels and nerves to the 

 ej'eball run. (The Ciliary Ganglion is shewn in Fig. 16.) The Optic Nerve, 

 flattened in the skull, leaves its foramen as a round cord, runs forwards and out- 

 wards — then inwards — and just before reaching the eyeball again slightly out- 

 wards. It thus describes an S-shaped curve (cf. Fig. 44). 



The connective tissue of the orbital fat forms near the eyeball a strong 

 membrane — Tenon's Capsule — . The eyeball moves in this membrane, as if 

 this were a ball- and socket-joint. There is, however, no free space between the 

 eyeball and capsule, as the space is filled up by a delicate scaffold-like tissue. 

 Tenon's Capsule ends behind at the Optic Nerve, in front at the Fornix of the 

 conjunctiva: the eye muscles pass through slits in the capsule, which sends at 

 these points sheaths to surround the muscles; these sheaths blend with the 

 aponeurosis of the muscles. Internal to the Inner Rectus, Tenon's Capsule forms 

 a triangular cushion and thus blends with the fascia of HORNER's Muscle, the 

 lachrymal sac and the puncta lacrimalia 



At that point it is only indirectly — through the internal tarsal ligament 

 — attached to the wall of the orbit. At the outer angle of the eye the Capsule 

 is in relation with the walls of the recess which lodges the lower portion of the 

 Lachrymal Gland and with the external tarsal ligament by which means it becomes 

 attached to the bone. 



