LACHRYMAL APPARATUS. 359 



external rectus muscle. The palpebral portion is smaller, 

 lias a more dense capsule, and is only partially separated 

 from the orbital. It extends down as far as the orbital 

 edge of the cartilage of the upper lid. 



The tears, secreted by this gland, are conveyed away by 

 from six to twelve excretory ducts which pass, for a short 

 distance and nearly parallel beneath the conjunctiva, to 

 the upper margin of the tarsal cartilage, where they open 

 by separate orifices, in a curved line on the inner surface 

 of the upper lid. 



Function. To secrete the tears which moisten the eye- 

 lids and the eye. The tears consist, chemically, of water, 

 and about one per cent, of muriate of soda, and a yellow 

 extractive matter. 



Puncta Lachrymalia, (Fig. 104.) These are two small 

 orifices, situated upon the papillary eminence, seen at the 

 inner extremity of each ciliary margin. They are always 

 open, and form the commencement of the lachrymal canals, 

 which are one to each eyelid, proceeding from the puncta. 

 The superior is longer and more curved; it first ascends, 

 and then bends suddenly downward and inward to the 

 sac, entering at its anterior and orbital portion. The in- 

 ferior canal, at first, descends, and then turns abruptly 

 inward and a little upward, entering the sac at nearly 

 the same point with the upper canal. These canals consist 

 of dense and elastic structure, lined by mucous membrane, 

 and have the tensor tarsi muscle inserted into them. 



The lachrymal sac, (Fig. 104,) is situated in the groove 

 of the os unguis, bounded in front by the nasal process of 

 the superior maxillary bone. It consists of mucous mem- 

 brane, covered by a strong fibrous expansion from the 

 tendo oculi, which tendon crosses it transversely a little 

 above its centre, and is an important point to bear in mind 

 in opening this sac, for fistula lachrymalis. The tensor tarsi 

 muscle covers its orbital surface. On opening this sac, its 

 lower portion is found constricted, and continuous with the 

 nasal duct ; at this point there is sometimes found a semi- 

 lunar fold or valve, separating the two. The interior of 



