Abstract
No mentionable difference is observable between a 10th month human fetus and a human adult, in respect of the histology of the caruncula lacrimalis and the plica semidunaris.
The caruncula lacrimalis contains, beside numerous sebaceous glands and downed hair-follicles, in some cases MOLL's glands, accessory tear glands and small MEIBOM's glands, in its leep layer.
The superficial layer of the caruncle is made of mucous membrane of the same structure as that of the conjunctiva palpebralis adjacent to it. The epithelium is of staratified cylindrical type containing mucous cells throughout, even on the summit of the caruncle, CONTINO et al.'s statement notwithstanding, and the propria under it is composed of connective tissue full of fibrocytes in human fetus but of a reticular tissue rich in lymphocytes in adults.
From the above finding and in consideration of the absence of hair-follicles on the inner ridge of the lid-margin, the coruncula lacrimalis is not originated in the inner ridge of the lid-margin, as CONTINO has asserted, but it appears that the superficial layer of the caruncle is of the same mucous membrane as that of the conjunctiva palpebralis in origin and its deep layer is formed by subsidence of a part of the eyelid skin minus its epidermis and the papillary layer of its corium.
The mucous membrane of the plica semilunaris is of the same nature as that of the conjunctiva palpebralis and the caruncula lacrimalis, except that its propria of loose connective tissue contains far fewer colonies of lymphocytes than in the latter. On the summit of this plica or in the vicinity stand out some mucous folds containing propria of compact connective tissue rich in fibrocytes and very rich in blood vessels.
The part of the conjunctiva palpebralis adjacent to the caruncula lacrimalis is poorer in sensory innervation than its more lateral part (SETO). Accordingly, the mucous membrane of the caruncle forming an extention of this conjunctival part contains as few sensory fibres and unbranched or simple branched terminations fromed subepithelially by them as the latter. Of course, neither intraepithelial fibres nor glomerular end-bodies could be found herein.
Since in the deep layer of the caruncle can be found hair-follicles provided with sebaceous glands and downs, the nerve supply in this part is similar to that in common haired skin, but in quantity, the sensory fibres are much smaller than in other parts. These few sensory fibres run in hair-nerve bundles in company with vegetative fibres and most of them come into the SETO's so-called hair-nerve shields in the hair-follicle necks, to end in very simple plexus-like terminations. The terminal mode here is perhaps the simplest of all parts of haired skin. A small part of the sensory fibres depart from the hair-nerve bundles to run up along the sebaceous glands into the mucous membrane, to end there in the above-described simplest terminations.
Sensory fibres are found running into the mucous membrane of the plica semilunalis too, in a number somewhat larger than those supplied to the mucous membrane of the caruncula lacrimalis. But the number, after all, is severely limited by the paucity of sensory nerve elements common to all parts of the conjunctiva palperbralis. Their terminations are also very simply constructed, in no case going beyond the simplest unbranched type ending subepithelially, except in the special mucous folds containing compact connective tissue rich in blood vessels, where a large number of vegetative fibres and a small number of sensory fibres participate in forming relatively complex nerve plexus, of which the sensory fibres come out to form beside unbranched terminations also simple branched terminations. In the plica semilunaris were found no intraepithelial fibres, either,
The vegetative fibres, both in the caruncula lacrimalis and the plica semilunaris
