FIBKOUS TUNIC OF THE EYE. 



809 



Anterior chamber 

 Lens 



Iris 



Cornea 



Sulcus circularis corneas. 



Posterior chamber 

 Ciliary muscle-- 

 Ciliary process - 

 Spatia zonularia 



Vitreous^ 

 Ora serrata 

 Chorioid 

 Rectus muscle. 

 Retina 



FIG. 679. SECTION OF A PORTION OF THE BULB OF THE EYE SHOWING 

 THE SULCUS CIRCULARIS CORNER. 



is about '95 mm., of its peripheral part, about 119 mm. Its anterior surface is 

 covered with a stratified epithelium, continuous with that which lines the con- 

 junctiva ; its posterior surface 

 is directed towards the an- 

 terior chamber of the eye and 

 is in contact with the aqueous 

 humour. Its degree of curva- 



j cc i. J Sinus venosus sclerte 



ture varies in different indi- 

 viduals ; it is greater in youth conjunctiva 

 than in old age, and is, as a 

 rule, slightly greater in the 

 vertical than in the horizontal 

 plane ; it diminishes from its 

 centre to its circumference, 

 and is less on the nasal than 

 on the temporal side of the 

 anterior pole. The outline of 

 the anterior surface of the 

 cornea is almost circular, 

 measuring 11 mm. vertically 

 and 11 '9 mm. transversely ; 

 that of the posterior surface is circular and has a diameter of 13 mm. 



The tissue of the cornea is continuous posteriorly with that of the sclera, the 

 line of union being known as the sclero-corneal junction. Directly in front of this 

 junction the inner surface of the cornea projects in the form of a rounded rim ; 

 behind this rim, in the interval between the sclero-corneal junction and the attach- 

 ment of the iris, is a groove, the sulcus circularis cornese (Arthur Thomson) 1 (Fig. 679). 

 The outer wall of this sulcus is composed of a thin stratum of trabecular tissue 

 placed on the inner side of the sinus venosus sclerae. Between this trabecular tissue 



and the front of the circum- 

 ference of the iris is a narrow 

 recess which on section ap- 

 pears as an acute angle ; it is 

 named the filtration angle or 

 angle of the iris. 



Structure. The cornea con- 

 sists, from before backwards, of 

 the following strata, viz., (Fig. 

 680) : 



1. Epithelium corneae. 



2. Anterior elastic lamina. 



3. Substantia propria. 



4. Posterior elastic lamina. 



5. Endothelium of anterior 



chamber. 



1. The epithelium cornese is 

 continuous with that covering the 

 free surface of the conjunctiva and 

 consists of six or eight strata of 

 nucleated cells. Deepest of all is 

 a single layer of perpendicularly 

 arranged columnar cells, the flat- 

 tened bases of which rest on the 

 anterior elastic lamina, while their 

 opposite ends are rounded and 

 contain the nuclei. Superficial 

 to this layer are three or four 



strata of polygonal cells, the majority of which exhibit finger-like processes joining with the 

 corresponding processes of neighbouring cells ; the more superficial layers consist of squamous 

 cells. The thickness of this stratified epithelium is about 45 /* at the centre, and about 80 n at 

 the periphery of the cornea. 



Substantia 

 propria, in 

 which the 

 corneal cor- 

 puscles are 

 seen to be 

 spindle- 

 shaped on 

 section 



Posterior 

 elastic lamina 

 Endothelium of 

 anterior chamber 



FIG. 680. VERTICAL SECTION OF CORNEA (magnified). 



1 The Ophthalmoscope, September 1910, and July 1911. 



