ON THE STRUCTURE OF MACULA LUTEA. 71 



period obliterated, and the fibre thereby obtaining a clear border which 

 completes its development. 



This act is one which is believed to be met with in all vessels at their 

 origin, but is frequently modified in certain vessels afterwards viz., in 

 the annular vessel, according to Mohl, the rings of fibre in this vessel 

 are formed by the union of one coil or coils of the fibre, in its early 

 condition, and afterwards separating from the others, or adhering and 

 becoming perfect rings in the interior of the vessel. In the reticulated, 

 on various portions of the original spiral fibre, a granule becomes en- 

 larged in the line, and forms the starting point for a branch of fibre, 

 which connects the turns of the spiral together, in various portions, and 

 in various directions. In the dotted and scalariform vessels, the fibres 

 become so connected as to leave meshes or portions of the membranous 

 wall of the vessel without any deposit within and this spot so left, 

 constitutes the dot in the former, and the linear marking seen on the 

 walls of the latter. This dot is plain in all such kind of vessels, ex- 

 cepting those found in woody Exogens, where it possesses (from some 

 slight difference of structure) a central mark, making it analogous to 

 that on the woody tissue of coniferous plants, with which the author 

 thought it identical in structure, and probably in function, but only of 

 a smaller size. 



The paper was illustrated with numerous diagrams representing the 

 successive stages of the minute process described. 



XVIII. ON THE STRUCTURE OF THE MACULA LUTEA OF THE HUMAN 



EYE.* 



By Dr. Grube of Konigsberg. 



THE yellow spot in the human eye is situated on that precise point of 

 the retina which answers to the posterior point of the axis of the eye, 

 and is, therefore, the only part of the retina in which the eye perceives 

 with perfect distinctness (in direct vision) the figures represented on it ; 

 since the remaining surface serves, as is well known, only for very im- 

 perfect (indirect} vision. Of the structure of this yellow portion, 

 which is so much more delicate than the rest of the retina, that, from 

 its susceptibility of injury, it was for a long time conceived to be per- 

 forated, I have no precise knowledge. I have often examined it in the 



From Miiller's Archiv. fur Anatomie und Physiologic, Heft 1, p. 38, 1840. 

 Translated by Mr. G. F. Richardson 



