THE COKNEA. 259 



of the cornea! tissue run at right angles to one an- 

 other. These lines represent the " corneal tubes" of 

 Bowman. Their appearance is due to the fact that 

 the pressure exerted has been sufficient to force the 

 injecting fluid into the interstices between the con- 

 nective tissue bundles, pushing these asunder, and 

 burrowing its way through the soft ground substance 

 which unites the bundles and lamellae. And, since 

 the cell-spaces occur in this ground substance, the 

 existence of a slight enlargement or fusiform swelling 

 here and there on the tubes is accounted for. 



These corneal tubes then are to be looked upon as 

 purely artificial products, not corresponding with 

 any pre-existing channels in the tissue (except per- 

 haps when the fluid passes along the sheath of a 

 nerve). They are always obtained when any fluid 

 which is not able to penetrate into the cell-spaces is 

 forced into the substance of the cornea. They are 

 seen when mercury is injected by the puncture 

 method, and this is how they were first obtained by 

 Bowman; and if air be forced with a syringe into 

 the tissue a similar effect is produced. In all cases 

 the tubes cease abruptly at the corneo-sclerotic junc- 

 tion, where the connective tissue becomes denser and 

 has a less regular arrangement. 



Preparation 16. Parts at the junction of 

 the cornea with the sclerotic. The corneo-scle- 

 rotic junction, the ciliary muscles, and the iris are 

 all well seen in their relations to one another in a 

 meridional section of the part of the eye where they 

 are situated. The section may be made from the 

 anterior segment which we have assumed to have 

 been hardened in M tiller's fluid and in spirit (p. 247). 

 It is not necessary to embed this entire, but sufficient 

 to cut out with sharp scissors under spirit a piece 

 which includes all the parts above enumerated. The 

 piece is first placed in oil of cloves for a few minutes; 

 it is then transferred to cacao-butter, which is kept 

 just melted over a sand-bath, and is allowed to re- 

 main in this for fully two hours, so that the butter 



