From this explanation the bluish white ring round the cornea ought to exist more or less in all internal inflammations of the eye, unless obscured by vascularity of the conjunctiva in inflammation of the cornea. So it does ; but in persons of otherwise sound constitution and not of advanced age, the overlapping sclerotica is so transparent and sometimes also to so small an extent, that it is not strongly contrasted by the transparent cornea. It is otherwise the case, however, in certain persons, especially such as are advanced in life, in whom the encroach ment of the sclerotica and fully developed con junctiva on the cornea exists to a great degree and in a very opaque state, that the bluish white ring appears in the exaggerated distinct ness which has commonly attracted the notice of surgeons.
The condition of the eye necessary for the distinct appearance of the bluish-white ring round the cornea occurring principally in old persons of bad constitution, and these being the very persons in whom an internal inflamma tion of the eye very often presents what is called the arthritic character, are circumstances which readily explain the error of supposing the bluish white ring round the cornea diagnos tical of arthritic iritis.* III.—Lacrymal organs properly so called.
Under this head are comprehended : 1. The secreting lacrymal organs, or the lacrymal gland and its excretory ducts. 2. The derivative la crymal organs, or the passages by which the secretions of the lacrymal gland and of the conjunctival surface are drawn off into the nose, viz. the lacrymal points, the lacrymal canalicules, the lacrymal sac, and nasal duct.
The lacrymal gland and its ducts may be considered as a branched diverticulum of the conjunctiva; the derivative lacrymal organs, to use the expression of M. De Blainville, as nothing but the continuation of the conjunctiva and its anastomoses with the olfactive mem brane.
1. Secreting lacrymal organs.
Lacrymal gland,—Glandula lacrymalis; Fr. La glande lacrymale ; Ital. La glandula lagri male ; Germ. Die Thrdnendrrise.
When the lacrymal caruncle was supposed to filtrate the suceus lacrymalis, and the lacry mal points to excrete it, the lacrymal gland was called glandula innominata.
The lacrymal gland (fig. 13 ) consists of two masses, an upper and a lower. The upper mass, or glandala lacrymalis supe rior, lies in the lacrymal fossa, a depres sion of a size sufficient to receive the point of the thumb, situated in the roof of the orbit at its upper and outer angle, just within the overhanging outer extremity of the superciliary arch. The superior lacrymal
gland i/ of an oval or triangular shape about three-fourths of an inch in its longest diameter and about half an inch across. It is flattened from above downwards. Its upper surface is convex; its lower plane or concave. The thickest edge of the gland is turned outwards. The gland is of a reddish colour and is en veloped in a thin but dense cellular coat. The lower mass of the lacrymal gland, or glandula lacrymalis inferior, is a loosely connected ag gregation of lobules of the same glandular substance as the above. It was first described by the second Monro, who called the lobules, for distinction's sake, glandulce congregates.* The lower mass of the lacrymal gland is smaller than the upper, with which it is in con tact above, whilst below it extends to the outer part of the upper margin of the tarsal cartilage of the upper eyelid. It lies indeed in the substance of the upper eyelid at the outer part. It is seen shining through the conjunctiva in everting the upper eyelid.
Intimate structure of the lacrymal gland.— The lacrymal gland is what is commonly called conglomerate. It belongs to Miiller's com pound glands with canals of the ramified type. " In the arrangement of the secreting canals of the lacrymal glands," says Miiller,t " two principal forms are observed : the one is that which I discovered in the chelonian reptiles ; the other, that which prevails in birds and Mammalia. In the chelonia, the gland is formed of a number of club-shaped lobes, united together by means of the different ducts which run in their interior. The duct of each lobe is pretty uniform in diameter, and into it open an innumerable quantity of microscopical tufts of caeca, which are arranged around it at right angles like the foliage of a moss on its stem." In birds, in which the lacrymal gland is very small and situate at the posterior angle of the eye, and Mammalia, the secreting ca nals of the lacrymal gland are regularly branched and terminate in each acinus in a number of small cells. In birds these cells are very large ; and in them, and likewise in the horse, the cells can be filled with mercury from the efferent duct.