THE RETINA 



1061 



surface exhibits numerous radial folds running from the ciliary processes to near 

 the pupillary margin; a thick layer of black pigment covers it and curls around this 

 edge, so as to come into view all around the pupil as seen from in front. The 

 ciliary border of the iris is continuous with the front of the ciliary body, and there 

 it also receives fibres from the ligamentum pectinatum iridis; in other respects the 

 iris is quite free, merely resting on the front of the lens-capsule near the pupil. 



Its stroma [stroma iridis] is spongy in character, being made up of vessels covered by a thick 

 adventitia, running from the periphery to the pupillary border, with interspaces filled by branch- 

 ing pigment cells, which are particularly abundant near the front surface Deep m the stroma, 

 running around near the pupillary border, we find a broad flat band of smooth muscle-fibres, 

 constituting the m. sphincter pupillae. Immediately behind the vascular tissue lies a thin 

 membrane, consisting of fine, straight fibres running radially from the ciliary border to the 

 stroma behind the sphincter. The nature of these fibres was long in dispute, but they are now 

 accepted as being undoubtedly smooth muscular— and comprise the m. dUatator pupillae. 



Fig. 804. — Diagrammatic Horizontal Section of Eyeball and Orbit. 

 (After Fuchs, much modified.) 

 Periorbita green; muscle-fascia red; Tenon's capsule yellow. 

 Lower lacrimal punctum 



Cornea \ • Caruncle 



\ I Inner palpebral ligament 



Opening of Meibomian gland ' ' 



Anterior chamber 



Iris 

 Corona ciliaris 



Orbiculus ciliaris 



Chorioid with 

 venae vorticosae 



Outer check ligament 



Fovea centralis retinae 



Muscle-fascia 



Orbital blood-vessel 



Central retinal vessels in 

 optic nerve 



External rectus muscle _ 



Nasal process of 



upper jaw 

 Anterior limb of 

 inner palpebral 

 ligament 

 Lacrimal sac 

 Posterior limb of inner 

 palpebral ligament 

 with Horner's muscle 

 springing from it 

 Lacrimal bone 

 Process of muscle-fas- 

 cia to under surface of 

 conjunctiva 

 Ora serrata 

 Tendon of insertion of 



internal rectus 

 Inner check ligament 

 Periorbita 

 Orbital plate of ethmoid 



bone 

 Posterior lamina of 

 muscle-fascia lined 

 by Tenon's capsule 



Internal rectus muscle 



Optic nerve 



The m. sphincter pupillce and the ciliary muscle are supplied indirectly by the oculomotor 

 nerve through the ciliary ganglion. The dilatator pupillff is supplied by sympathetic fibres, which 

 have their origin from the cells of the superior cervical gangUon. Thence they ascend in the 

 carotid and cavernous plexuses, and join the ophthalmic division of the trigeminal nerve, passing 

 to the eyeball by way of the long ciliary nerves. The pre-ganglionic sympathetic fibres leave the 

 spinal cord by the motor roots of the first two or three thoracic nerves, and ascend the sympa- 

 thetic trunk to the superior cervical ganglion without interruption. 



The posterior surface of the iris is lined by pigment already mentioned, consisting of two 

 layers of pigmented cells, each layer representing the extension forward of one subdivision of 

 the retina. The anterior surface of the iris is covered by a delicate epithelial layer, continuous 

 with the cells of the posterior elastic lamina of the cornea. The colour of the ins in 

 different individuals depends upon the amount of stromal pigment. 



3. The retina. — The inner surface of the vascular coat is everywhere lined by a 

 layer of pigment of corresponding extent, which usually adheres to it closely on 

 dissection. 



