Efferent or excretory ducts of the lacrymal glands.—The lacrymal glands pour out their secretion by nine or twelve very slender excre tory ducts which proceed above down wards and open on the surface of the con junctiva on the inside of the upper eyelid. The orifices of the ducts are placed at about one-twentieth of an inch apart from each other in a row extendinz about half an inch from the outer cauthus inwards, parallel to but a little above the outer part of the upper margin of the tarsal cartilage, that is, at the inferior boun dary of the lower mass of the gland.
The excretory ducts of the lacrymal gland were first discovered on the 11th of November, 1665, by Nicolaus Steno,* in the eyelid of a sheep. He delineated them from the eye of the calf. Moreover it appears that Steno de scribes vasa lacrymalia discovered in man, which opened in the membrane of the upper Admitted by some and doubted by others from the time of Steno, the ducts of the lacry mal gland became a subject of dispute between Dr. William Hunters and the second Monro,§ the one claiming to have observed them in the human eye before the other.
The best way to demonstrate the ducts is to stretch the upper eyelid, turned inside out, upon the finger; then wipe clean the surface of the conjunctiva, and having by close in spection at the place where the ducts open, as above described, discovered the orifices, take a short piece of human hair in the point of a forceps, and entering it at the orifice, push it on in the direction of the duct. From the orifices on the surface of the conjunctiva the ducts run nearly parallel with each other upwards.
Of two eyes before me I have in this way inserted hairs into nine orifices of ducts in the one and into twelve orifices of the other, a work which did not occupy five minutes for each eye. In both eyes there is one orifice of a duct exactly within the external commissure, and another rather within the lower eyelid Scefigs. 12 & 14.
The preceding description of the lacrymal gland and its ducts shows that the latter and the lower mass at least of the former may be readily wounded along with the upper eyelid, and that in Crampton's operation for entro pium, the lower mass of the gland, together with some of the lacrymal ducts, must neces sarily be wounded, if the eyelid be cut through near the outer angle and to any height. In cases in which I have performed the operation, however, I have not observed any lacrymal fistula or other bad consequence follow.
Tears.—Lacryme, Fr. Les larmes ; Ital. Le lagrime ; Germ. Die Thriinen. The lacry mal secretion like the salivary appears con stantly to flow, though in no greater quantity than is sufficient to moisten the surfaces of the conjunctiva. The derivative lacrymal organs are in this case equal to the removal of it; but when the tears are poured out in unusual quantity, as they are, like the salivary or uri nary secretion as well as that of the skin, in certain affections of the mind, they run over the margin of the lower eyelids and drop down the cheeks.
According to Fourcroy and Vauquelin there remains after evaporating the tears, about one per cent. solid substance, which consists chiefly of common salt and a yellow extractive matter perfectly soluble in water. Before drying, this appears quite similar to mucus.
2. Derivative lacrymal organs.
Previously to describing the passages by which the tears are drawn off into the nose, it will be advantageous to take a glance at the osseous groove and canal in which the prin cipal part of those passages is lodged.
Osseous groove for the lodgement of the lacrymal sac. The lacrymal groove, sulcus la crymalis, is situated at the fore part of the inner wall of the orbit. It is directed from above downwards, extending from the junc tion of the frontal bone with the nasal process of the superior maxillary and with the lacrymal bone, on the one hand, and to the inner and lower angle of the margin of the orbit on the other. here it runs into the osseous canal for the nasal duct. The lacrymal groove is pretty deeply scooped out, and is about eight-tenths of an inch long and five-twentieths broad.
The outer aspect of the nasal process of the superior maxillary bone is divided by an as cending ridge, the continuation of that forming the lower margin of the orbit, into two sur faces. The posterior surface, which is the narrower, forms the anterior half of the lacry mal groove. The posterior half of the groove is formed by that narrow grooved part of the orbital surface of the lacrymal bone in front of its vertical crest. The line of junction (shin dylesis) between the posterior margin of the nasal process of the superior maxillary bone and the anterior margin of the lacrymal runs down longitudinally in the bottom of the •groove.