DISSECTION OF THE HEAD AND NECK. 177 



there occur in the lower lid some long tactile bristles. The inner or 

 ocular surface is lined by the conjunctival membrane, and is moulded on 

 the front of the eye. If the upper lid be everted there will be fouud on 

 its inner surface, near the outer angle, a number of minute openings, 

 into which bristles should be passed. These are the openings of the 

 excretory ducts of the lachrymal gland. On the same surface, but near 

 the opposite angle, and close to the free edge in each lid, there is a 

 round opening of larger size, but still minute. These are the puncta 

 lachrymalia, the orifices of the lachrymal ducts, by which the lachrymal 

 secretion is conveyed away from the eye. The free borders of the eyelids 

 circumscribe the palpebral fissure, which is a mere line when the eye is 

 closed, but is ovoid or elliptical, with the long axis directed obliquely 

 upwards and outwards, when the eye is open. The free edge of each lid 

 is somewhat stiff, this stiffness being due to a slender rod of cartilage 

 which extends along it. The meibomian glands are lodged in depressions 

 on the ocular surface of this cartilage, and may be seen through the 

 conjunctiva as close-set yellow lines having a direction at right angles to 

 the edge of the lid. They number about fifty or sixty in the upper lid, 

 but they are fewer and less distinct in the lower. Each gland consists 

 of a main tube with lateral sacculi opening into it on each side, and it 

 discharges its secretion by a dot-like orifice on the edge of the eyelid. 

 The free edge of each lid carries a fringe of stiff hairs — the eyelashes, 

 which tend to prevent the entrance of foreign particles into the eyes. 

 The attached edge of each lid is marked on the ocular side by the angle 

 of reflection of the conjunctiva from the lid' to the eyeball, but on the 

 facial side the eyelid passes into the surrounding skin without any 

 defined line. At each extremity the eyelids join to form a commissure, 

 or cant hies. The outer or temporal canthus is acute, but the inner or 

 nasal canthus is rounded, and lodges the caruncula lachrymalis. 



The Caruncula Lachrymalis is a small, rounded, and, generally, 

 dark-pigmented nodule placed within the nasal canthus, and about 

 equidistant from the two puncta lachrymalia. It is covered by con- 

 junctiva, and is composed of connective-tissue with some mucous 

 follicles and the bulbs of a few short, hairs, which project from it. 



The Membrana Nictitans. This body is placed at the inner canthus, 

 where, ordinarily, it projects to only a slight extent, but it is capable of 

 being thrust more than half way across the front of the eye. It has for 

 its basis a thin and flexible piece of elastic cartilage, which anteriorly is 

 invested by conjunctiva. Posteriorly this cartilage passes to the inner 

 side of the eyeball, where it becomes connected with the cushion of 

 semifluid fat which is found in the posterior part of the orbit. The 

 membrana nictitans has no muscle to move it directly ; but when the 

 eyeball is retracted within the orbit it presses on the semifluid fat 

 behind it, and this, tending to escape at the side of the eyeball, pushes 



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