THE EYE AND ITS APPENDAGES. 



175 



terior surface of the lids, discharging by numerous orifices along the 

 edges of the lids a viscid fluid which prevents the overflow of 

 tears at night. 



Caruncula lachrymalis.'^ — A small, red elevation, in the internal 

 canthus, about the size of a grain of wheat ; consisting of an aggre- 

 gation of small glands, and often furnished with hairs. 



Lachrymal gland? — A lobulated gland, about the size of a filbert, 

 and of a light pink colour, situated in a fossa on the roof of the 

 orbit, near the external angular process. It consists of two portions, 

 viz., orbital and palpebral. It discharges tears by ten or twelve 

 ducts,* whose orifices open upon the upper and outer part of the 

 conjunctiva. 



Lachrymal canals. — These open by two small orifices upon a 

 papilla at the inner part of each lid, called puncta lachrymalia,^ 

 The tears enter these orifices 



and are conveyed along a bent Fig. 152. 



canal into the lachrymal sac. 



Tensor tarsi or Horner'^s 

 muscle. — (Fig. 152.) — Arises 

 from the os unguis,* and is in- 

 serted by two divisions* into 

 the orifices of the lachrymal 

 canal. Its nasal face adheres 

 to the lachrymal sac. 



Lachrymal sac and nasal 

 duct. — Is a continuous tube 

 contained in the passage formed by the nasal process of the superior 

 maxillary, the unguiform, and inferior turbinated bones. Its external 

 coat is fibrous, and its internal mucous ; it is larger above than it is 

 below, and opens into the inferior meatus of the nose. The mucous 

 lining forms a semicircular fold or valve. 



The muscles: Levator palpehrce si^perioris.* — Origin, near the 

 optic foramen. Insertion, by a broad aponeurosis into the upper lid. 

 It draws the lid upwards. 



The four straight 'muscles, arise around the optic foramen ; and 

 are inserted, by tendinous ex- 

 pansions, within a few lines '^* 

 of the cornea. They are 

 called superior,^ inferior,*^ in- 

 ternal, *° and external.** 



The superior oblique rrtus- 

 cle,^ arises from the edge of 

 the optic foramen, and plays 

 over a tendinous pulley^ upon 

 the orbitary ridge of the fron- 

 tal bone ; is inserted into the 

 sclerotica beneath, and beyond the superior rectus. 



