i5o8 A MANUAL OF ANATOMY 



the sclerotic is pierced by four openings for the passage of the 

 vencB vorticoscB of the choroid. 



The sclerotic is thickest posteriorly around the optic entrance. 

 It is also thick near the corneo-scleral junction, where it gives 

 insertion to the recti muscles, from the tendinous expansions of 

 which it receives accessions of fibres. 



The outer surface of the sclerotic is covered by a membranous 

 investment, called the capsule of Tenon, and between the two there 

 is the perisclerotie lymph-space or Tenon's space, which is broken 

 up into a reticulum by processes of connective tissue which pass 

 between the capsule of Tenon and the sclerotic. This space com- 

 municates with the subdural and subarachnoid spaces. The inner 

 surface is of a dark brown colour, and presents grooves for the 

 ciliary vessels and nerves. It is lined with connective tissue 

 containing pigment cells, this layer being called the lamina fusca. 

 Processes from this layer pass to be attached to the choroid coat, 

 and these processes, together with vessels and nerves, traverse an 

 interval, which represents the perichoroidal lymph-space. This 

 space communicates with the perisclerotie lymph-space through 

 the vascular openings in the sclerotic. Anteriorly the sclerotic 

 blends with the cornea at the corneo-scleral junction, the sclerotic 

 slightly overlapping the cornea. Posteriorly, around the optic 

 entrance the sclerotic blends with the dura-matral sheath of the 

 optic nerve. 



Structure. — ^The sclerotic is composed of fibrous tissue, mixed 

 with elastic fibres, and it contains many connective-tissue cor- 

 puscles. The fibres are arranged in bundles, which are disposed 

 longitudinally and transversely, and interlace with one another. 

 The connective-tissue corpuscles occupy spaces between the fibres, 

 which may be regarded as lymph-spaces. 



Arteries. — These are the short ciliary group of posterior ciliary 

 arteries, and the anterior ciliary arteries, which are branches of 

 the ophthalmic artery. The vessels belonging to the former group 

 are disposed in the form of capillary networks ; whilst the vessels 

 derived from the latter form a ring near the corneo-scleral junction 

 beneath the conjunctiva, to which ring they converge in the sub- 

 stance of the sclerotic. 



The sclerotic veins open into the anterior ciliary veins, and into 

 the vencB vorticoscB of the choroid. 



Nerve-supply.— The ciliary nerves. 



The capsule of Tenon will be found described on p. 1151. 



Cornea. — ^The cornea is the transparent part of the external 

 coat of the eyeball, of which it forms the anterior sixth, and it 

 serves to transmit light. It is almost circular, its transverse 

 measurement being slightly greater than the vertical. At its cir- 

 cumference it is continuous with the sclerotic, by which it is slightly 

 overlapped. The anterior surface is convex. The posterior surface 

 is concave, and forms the anterior boundary of the anterior chamber 

 of the eye. 



