204 The Bye of the Cod-fish. 



the minuteness of the vessels not permitting a clear picture of 

 their disposition had they been drawn of the natural size. In 

 the several instances in which I have thus treated the eye, I 

 have never found the colours to pass into the vascular con- 

 tinuation of the true choroid beyond the' band, neither into 

 the band itself, nor even, so far as I can remember, into the 

 membrana Ruyschiana ; and thus it is seen that naked-eye 

 experiences taken by themselves are calculated to convey the 

 idea of the non-vascularity of the so-called gland. By a series 

 of careful microscopic investigations, however, I have satisfied 

 myself as to the inaccuracy of this inference, and I therefore 

 now proceed to show what is the true character of the structure 

 in question. 



If a thin vertical or horizontal section be removed from the 

 choroid band, and placed under a quarter-inch objective, the 

 smaller arterial and venous branches will be seen to divide 

 suddenly into multitudes of minute capillaries, the latter taking 

 their origin at a point precisely corresponding with the clearly- 

 defined line of limitation indicated by the stoppage of the 

 artificially-introduced pigments. These small vessels are closely 

 connected to one another by their own walls, and not by the 

 intervention or extension of any fibres from the connective 

 elements of the choroid. They are all arranged in a simple, 

 linear, parallel manner, and their width does not appear 

 to exceed that of the short diameter of the blood corpus- 

 cles, the admeasurements of the latter being about the 1 -2500th 

 of an inch long, and the l-3500th of an inch in breadth. In 

 fresh eyes the capillaries are always found gorged with blood, 

 and when I recently succeeded in isolating, more or less com- 

 pletely, a few of the vessels of the band, one of them was seen 

 to contain blood corpuscles arranged in single file. As shown 

 in the accompanying diagram (Fig. 6), the capillaries are straight 

 and of uniform diameter throughout; moreover, they do not 

 give off any branches or dilatations such as are found to occur 

 in the true erectile structures. 



From beneath the external border of the horseshoe-shaped 

 band the outer vascular choroid is supplied with numerous 

 vessels, which for the most part proceed in a radiating manner 

 to the circumferential border of the choroidal membrane. Those 

 vessels are obviously a continuation of the reunited capillaries 

 of the band, but their mode of oi'igin is not so easily seen at 

 the outer as at the inner border of the band. As previously 

 remarked, a simple fibrous layer is interposed between the 

 choroid proper and the membrana Ruyschiana, the latter being 

 also fined internally by another non-vascular membrane, winch 

 is entirely destitute of fibres (Fig. 7). This membrane is ap- 

 plied against the baccillary layer of the retina, and consists of a 



