The intimate nature of the connexion between the tarsal cartilages and the conjunctiva which lines them has been already noticed. Beyond the tarsal cartilages the adhesion of the palpe bral conjunctiva becomes looser and looser until its transition into the ocular conjunctiva.
The ocular conjunctiva is smoothly spread over the front. of the sclerotica, where it first passes on the latter. The interposed cellular tissue is loose enough to allow it to slide upon the sclerotica, or even to be raised up in wrin kles according to the motions of the eyeball, which are thus facilitated. But as the con junctiva approaches the cornea it is more and more closely applied to the sclerotica and con sequently less readily falls into wrinkles. The debated question of a conjunctival covering of the cornea will be considered when speaking of the intimate structure of the conjunctiva.
The cellular tissue between the conjunctiva and sclerotica is sometimes the seat of extrava sations of blood, subconjunctival ecchymosis, sometimes the seat of an accumulation of se rous fluid, as in the oedema attending erysipela tons ophthalmia. It is sometimes the seat of a more serious, form of oedema, that known by the name of chemosis, and common in the purulent inflammation of the conjunctiva. It may also be the seat of emphysema, and is occasionally so of phlegmon.
Nature of the conjunctiva.—The conjunctiva forms part of that membraneous system, conti nuous with the skin at all the natural apertures of the body, which lines the interior of the respiratory and digestive canals, and to which, as to that lining the genito-urinary passages, the generic name of mucous membrane is given. Of course different parts of this system present specific peculiarities in structure and function, and this is the case even in regard to the palpe bral and ocular parts of the conjunctiva, though so near each other. Some of the Germans have unnecessarily involved this subject. Thus Walther viewed the conjunctiva as mucous in the eyelids, tegumentary over the sclerotica, and serous over the cornea. Whence we some times meet in their ophthalmological works such expressions as " the conjunctiva considered as a mucous membrane," and " the conjunctiva considered as a serous membrane." In refe
rence to these opinions of his countrymen, Miiller* has thought it necessary to remark that the conjunctiva is as certainly a mucous membrane as any other of which the character has not been doubted. * • On the other hand it has nothing in common with the serous membranes either in secretion, for the limpid secretion of the eyes is derived from the lacry mal gland, or in its form, which is not that of a shut sac.
Within the upper eyelid towards the outer canthus (fig. 12f), the conjunctiva presents the minute mouths, nine or twelve in number, of the ducts of the lacrymal gland. At the inner canthus the conjunctiva is continuous through the lacrymal points with the membrane lining the canalicules, and so through them, the la crymal sac and nasal duct, with the mucous membrane of the nose. At the margin of the eyelids its continuity with the skin is seen.
The oculNRalpebral space of the conjunc tiva receives the tears much in the same way that the mouth receives the salivary secretions. Like other mucous membranes the conjunctiva secretes a mucous fluid which lubricates its surface and serves to protect it from the irri tating action of external agents, and even from that of the lacrymal secretion which is naturally poured out on it.
Intimate structure of the conjunctiva.
Palpebral conjunctiva, conjunctiva palpe braruns.—The conjunctiva lining the eyelids is thicker and more vascular than that which invests the sclerotica. On the posterior surface of the eyelids, about one-twelfth of an inch from and parallel with the posterior acute edge of the margin, there is a very slight groove. Between this and the edge of the eyelid the conjunctiva is sufficiently distinct by its moist shining surface and its vascularity, from the more integument-like though delicate invest ment of the margin of the eyelids with which it is continuous. - But it is immediately in the groove and especially beyond it that the con junctiva, as pointed out by Eble,-1- first shows itself truly as a mucous membrane, that is, pre sents all the characters commonly ascribed to mucous membranes.