414 CORNEA. 



rotica to be distinct from each other. And although their 

 structure is essentially different in the human species, it is much 

 more so in some fishes and in some birds. 



The cornea is about six lines in its longest or transverse 

 diameter, and is a section of a spheroid, the diameter of which 

 would be seven lines and a half. Its thickness is nearly equal 

 throughout ; varying from a half to the three quarters of a line. 

 Mr. Ramsden and Sir E. Home assert, that it is rather thickest 

 in the centre. On the inner face of the cornea, at its junction 

 with the sclerotica, there is a slight groove, where the iris meets 

 the ciliary ligament and is attached in contact with it. This is 

 for the lodgment of a small vein, called the sinus circularis 

 iridis or canaliculus Fontana, which communicates with the 

 anterior ciliary veins. Branches from the ciliary nerves have 

 latterly been traced into the cornea by Schlemm and others. 

 According to Professors Knox, Cloquet, and Jurine, the most 

 internal layer of the cornea is united to the iris by short fibres, 

 which have something of a tendinous appearance, and by which 

 they think the contraction of the iris, augments the convexity 

 of the cornea. Professor Jacob considers this internal layer 

 of the cornea, (placed immediately in front of the lining mem- 

 brane of the aqueous humor,) as a peculiar layer of semi- 

 cartilaginous matter, like the capsule of the lens ; the office of 

 which is to preserve the proper curve of the cornea ; and 

 which he has named the elastic cornea. He considers it as 

 terminating behind, by slipping in between the ciliary liga- 

 ment and sclerotica. It is this membrane, he thinks, which 

 forms the protruding pouch in ulcerations of the cornea. 

 Ramsden and Home, assert that the tendons of the recti 

 muscles are inserted into the layers, or rather expanded over 

 the surface of the cornea ; by the action of which the cornea 

 may be flattened. This, however, is but a revival of the opin- 

 ion of Morgagni and Briggs, which was refuted by Zinn . 



From what has been already stated, it appears that there 

 are pores in the cornea, through which the fluid situated 

 between its lamina may be pressed. 



It is probable that an exhudation through these pores takes 

 place after death, as a pellicle then forms on the cornea, which, 



