1058 



SPECIAL SENSE ORGANS 



forward. Observe that the iris, the cih'ary processes, etc., and the chorioid are all different 

 parts of the same ocular tunic — mere local modifications of it. Similarly the sclera and cornea 

 are seen to blend together to form one outer coat. 



An eyeball should now be placed for half an hour in a freezing mixture of crushed ice and 

 salt. It will thus become quite hard, and should at once be divided into two parts by cutting 

 it antero-posteriorly through the centre of the cornea and the optic nerve. We thus gain another 

 view of the relations of parts, the position of the lens between the aqueous and vitreous chambers, 

 etc. On removing the lens, vitreous, and retina, and brushing off its pigment, the light markings 

 corresponding to the chorioidal veins (venae vorticosse) should be noted, and their distribution 

 studied. Usually four vortices or fountain-like markings are found in the whole chorioid, 



Fig. 802. — Horizontal Section of the Eyeball. X 4. 



Optic axis 

 Corneal epithelium 

 Posterior surface of cornea '^^ 

 Cornea \ 



Anterior surface of lens 

 ! Crystalline lens 



Iris 



Zonula ciliaris 



Posterior 

 surface of 

 lens 



Sulcus scleras 

 / Lig. pectinatum iridis 

 J / Posterior chamber 



I I / Sinus venosus scleras 

 ■' /^Scleral conjunctiva 



z'"^'^';,- Anterior chamber 

 ^<s^- '"^=;^^.- Angulus iridis 



Ciliary muscle 



~ Ciliary body 



Ciliary processes 

 Zonular fibres 



Papilla of optic nerve 



Lamina cribrosa sclerae 



A. Centralis retinae 



Retina 

 Chorioidea 

 Macula latea and fovea centralis 

 Sclera 



Ml "Sheath of optic nerve 

 Intervaginal space 



their points of junction situatcMl at ai)])roximately equal distances from one another at about 

 the line where the posterior and middle thirds of the globe meet. These sections should be kept 

 for reference while following the further description of the ocular tunics. 



The coats of the eyeball. — 1. The outer, fibrous coat of the eye [tunica 

 fibrosa oculij is formed by the sclera and cornea, which pass into one another 

 at the scleral sulcus. It consists throughout mainly of fine connective-tissue 

 fibres, arranged in interlacing bundles, with small lymph-spaces at intervals 

 between them. The naked-eye appearance of the two divisions of this fibrous 

 coat is, however, quite different, the cornea being transparent, while the sclera 

 is white and opaque. 



The sclera encloses the posterior five-sixths or so of the eyeball. It is perfo- 



