fold, is towards the cornea. The rolling of the 
___ eyeball outwards has a tendency to undo the 
_ fold, which on the contrary is rendered more 
distinct when the cornea is turned towards the 
“nose. In quadrupeds the semilunar fold is 
_ much more developed, and contains within it 
__ amore distinct cartilaginous plate. It consti- 
tutes what in them is called membrana nictitans. 
_ The third eyelid in birds is the same structure 
carried to its highest pitch of development. In 
“man, in whom it is very small, its component 
_ Structures are readily developed to a consider- 
able size by inflammation. According to Soem- 
Terring the semilunar fold is larger in the 
We shall have occasion to recur to 
the membrana nictitans of quadrupeds and the 
third eyelid of birds. 
___ The intimate nature of the connexion between 
the tarsal cartilages and the conjunctiva which 
Tines them has been already noticed. Beyond 
the tarsal cartilages the adhesion of the palpe- 
conjunctiva becomes looser and looser 
until its transition into the ocular conjunctiva. 
The ocular conjuictiva is smoothly spread 
the front. of the sclerotica, where it first 
s 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- 
_ Tous fluid, as in the edema attending erysipela- 
| tous ophthalmia. It is sometimes the seat of a 
ity more serious form of cdema, that known by 
i _ 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- 
heegroes. 
| nuous with the skin at all the natural apertures 
of the body, which lines the interior of the 
| tespiratory and digestive canals, and to which, 
i as to that lining the genito-urinary passages, 
} 
f 
_ the generic name of mucous membrane is given. 
_ Ofcourse 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 neareach other. Some of the Germans have 
_ unnecessarily involved this subject. Thus 
_ Walther viewed the conjunctiva as mucous in 
the eyelids, tegumentary over the sclerotica, 
ind 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- 
Tence to these opinions of his countrymen, 
<x 
1 = 
ee 
——_ 
LACRYMAL ORGANS. 
85 
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. 12,f'), 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 oculdpalpebral 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- 
brarum.—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,+ first shows 
itself truly as a mucous membrane, that is, pre- 
sents all the characters commonly ascribed to 
mucous membranes. 
The palpebral conjunctiva consists of a 
chorion, the free surface of which presents 
papillz, constituting what is called the papillary 
body, and the whole is covered by anepithelium. 
The chorion of the palpebral conjunctiva is 
intimately incorporated with the tarsal fibro- 
cartilages, so that the latter and their investing 
conjunctiva might be considered together as 
constituting a compound or fibro-mucous struc- 
ture. Beyond the cartilages the chorion ap- 
pears in its independent and separable form as 
a felt-work composed of an interlacement of 
filamentous cellular tissue, and is the nidus for 
the ramification of the vessels and nerves. 
Papillary body—If the upper eyelid be 
* Handbuch der Physiologie des Menschen, 
Bd. i, S. 429, Coblenz, 1838, or Translation by 
Baly, p. 436. : , 
+ Ueber den Bau und die Krankheiten der Binde-~ 
haut des Anges,p. 9. Wien, 1828. 
