APPENDAGES OF THE EYE. 209 



Short Ciliary, some 20 in number, arise from the Ciliary Ganglion [See ante, 



page 137], pierce the sclerotic and go to the ciliary muscle, choroid, iris, 



cornea, and to the sheath of the optic nerve. 

 Ascending, from Meckel's ganglion [See ante, page 137], enter the orbit by 



the spheno- maxillary fissure, going to the optic nerve, the 6th nerve, and the 



ciliary ganglion. 



Describe the formation and course of the Optic Tract. The fibres 

 which form the optic tract have their deep origin in the optic thalamus, corpora 

 geniculata, and the anterior corpora quadrigemina. The tract winds around the 

 crus cerebri as a flattened band, receiving from the crus a few fibres of attach- 

 ment, and also fibres from the lamina cinerea and the tuber cinereum. In 

 front of the latter body the two tracts join to form the Optic Commissure or 

 Chiasm. [See 2 on Fig. 61, page 130.] 



What is the arrangement of the Fibres in the Optic Commissure ? 

 As generally described, the fibres undergo a partial decussation, as follows, 

 viz., the 



Decussating Fibres, are the most numerous. They lie in the centre of the 

 commissure, and pass across to the opposite side, connecting the retina of 

 each eye with the opposite cerebral hemisphere. 



Longitudinal Fibres, are the external fibres in the optic tracts, passing 

 into the optic nerve of the same side, connecting each retina with the 

 cerebral hemisphere of its own side. 



Inter- cerebral Fibres, situated posteriorly in the commissure, passing from 

 one optic tract to the other. 



Inter-retinal Fibres, lie anteriorly in the commissure, passing from one 

 optic nerve to the other, and connecting the retina of one eye with that 

 of the other. 



Describe the Optic Nerve. The Optic Nerve proper is the 2d cranial 

 nerve, arises from the optic commissure, passes into the orbit by the optic fora- 

 men in company with the ophthalmic artery, is pierced by the central artery 

 of the retina, and enters the eyeball posteriorly -^ inch inwardly from its axis, 

 piercing the sclerotic and choroid coats, and finally expanding in the retina. 

 It is surrounded by a tubular process of dura mater, which as the nerve enters 

 the orbit, subdivides to form both the sheath of the nerve and the periosteum 

 of the orbit. 



APPENDAGES OF THE EYE. 



What are the Tutamina Oculi ? They are the appendages of the eye, 

 including the 



Eyebrows, or Supercilia. Lachrymal Gland, and Ducts. 



Eyelids, or Palpebrae. Lachrymal Sac. 



Conjunctiva, or lining membrane. Nasal Duct. 



