15. =Puncta lachrymalia.=--The puncta lachrymalia are distinctly visible at the inner angles of the lids. The lower punctum is larger and a little more external than the upper, so that they are not exactly opposite. The direction, too, of the puncta deserves notice. Their open mouths look a little backwards, ready to imbibe the tears. When their proper bearing is lost, as in facial paralysis or by a cicatrix near the lid, the tears overflow the cheek. The length of the lachrymal canals is from three to four lines. The lower is a little shorter and wider than the upper. As each makes a little angle in its course, about a line from its orifice, the lid should be drawn outwards to straighten the canal when we introduce a probe. 16. =Lachrymal sac.=--To find the lachrymal sac, draw outwards the eyelids to tighten the tendo oculi, which crosses the sac a little above its middle. A knife introduced just below the tendon close to the edge of the orbit would enter the sac. The angular artery and vein would be on the inner side of the incision. A probe directed in a line with the inner edge of the orbit, _i.e._ downwards, outwards, and backwards, would pass down the nasal duct, and appear in the inferior meatus of the nose. The tendo oculi serves many purposes besides giving attachment to the cartilages and muscles of the lids. One purpose is said to be to pump the tears into the lachrymal sac. Place a finger on the tendon, and feel that it tightens every time the lids are closed. The tendon, being intimately connected to the sac, draws, as it tightens, the sac wall outwards and forwards, and in this way it may pump along the lachrymal canals any fluid collected at the angle of the eye. 17. =Nasal duct.=--The nasal duct is from six to eight lines long, and narrowest in the middle of its course. Its termination in the inferior meatus lies under the inferior spongy bone, about a quarter of an inch behind the bony edge of the nostril. The appearance of the orifice in the dry bone conveys no idea of its size and shape in life; for it is diminished by a valve-like fold of mucous membrane, so that it becomes, in most cases, a mere slit, not exceeding a line in diameter.