THE SENSES. 261 



Nerves : they are branches oftrigeminus (frontal., lacrymal., infraorbital., 

 infratrochlearis) ; facialis (to m. orbicular.) ; oculomotorius (to levat. palpe- 

 brar.) 



493. The glands of the eyelids. 



a. The glands of Meibomius, gl. Meibomiance, lie in the substance of the 

 tarsal cartilages (twenty to twenty-five in the inferior, thirty in the superior), 

 are rather lower than the last, and open on the posterior edge of the free 

 border of the lid, in a row. Each gland consists of a convoluted tube, the 

 walls of which are cellular all round, so that it looks like a bunch composed 

 of berries united together without stalks, is formed of uniting tissue, filled 

 with flat cells and fat vesicles, and pours out a viscous fluid which prevents 

 the overflow of the tears (lema). The short excretory duct of one gland some- 

 times unites with that of another, or is fissured. 



b. Caruncula lacrymalis, is a flesh-like corpuscle, the size of a grain of 

 rye at the internal canthus, internal to plica semilunaris, covered by the con- 

 junctiva ; it consists of an assemblage of glandules of the same kind as the 

 Meibomian, from which (seven or eight) minute openings proceed, and upon 

 which light, short, small hairs are seen. 



494. 4. The lacrymal organs, organa lacrymalia. 



a. The lacrymal gland, glandula lacrymalis (innominata), consists of two 

 parts, both of which are situated above the external canthus. 



The superior or orbital portion, of the size of an oat grain, lies transversely 

 with the superior convex surface attached to ihefovea lacrymal. of the frontal 

 bone, with the inferior concave surface upon m. rectus externus ; its anterior 

 border close behind the superior external border of the orbit, and the upper 

 lid ; on its posterior border nerves and vessels enter. 



The inferior or palpebral portion is smaller, thinner, situated, covered by 

 a fibrous membrane, upon the external side of the upper lid, and reaches 

 downwards almost to the superior border of the tarsus superior. The ten or 

 twelve excretory ducts of both parts open (almost invisibly) on the posterior 

 surface of the upper lid, one line above the cartilage, from the external angle 

 as far as the centre of the lid, in a row, and perforate the conjunctiva. Arter. : 

 art. lacrymalis. Nerves : a branch of sympathicus ; n. lacrymal. (trigemin.) 

 passes, nominally only, through it to the conjunctiva, like n. facialis in the 

 Parotis. 



b. The puncta and lacrymal canals. The circular, constantly open punc- 

 tum lacrymali, is found at the apex of a small tubercle (papilla lacrymalis) on 

 the internal part of the free border of the eyelid. The superior looks down- 

 wards and backwards, the inferior upwards and backwards towards the 

 globe. Both lead into the lacrymal canaliculi, canaliculi lacrymales a. cornua 

 limacum. They pass at the commencement vertically, immediately bend at 

 a right angle, inside the free border of the eyelids, inwards and open, inde- 



