18 ANATOMY OF THE HEAD AND NEC 1C. 



has an opening at the inner extremity of each eyelid, indi- 

 cated by a slight prominence, in the centre of which is a 

 small orifice called the punctum lacrymale. The canals of 

 the two lids uniting form a common canal, less than one- 

 eighth of an inch in length, terminating in the lachrymal 

 'sac, which occupies the concave portion of the lachrymal 

 bone. This sac is the expanded upper part of the nasal 

 duct, which conve3 7 s the tears from the lachrymal canals to 

 the inferior meatus of the nasal fossa (p. 65). In the inter- 

 nal commissure of the eyelids there is a prominent reddish 

 body formed from the conjunctiva, and called the carun- 

 cula lacrymalis ; just external to this is a fold of the con- 

 junctiva, called plica semilunaris, in which may sometimes 

 be found a minute cartilage ; this is considered as corres- 

 ponding to the third lid or membrana nictitans of birds. 



The eyelids are supplied by the palpebral arteries, 

 branches of the ophthalmic, given off near the inner angle 

 of the orbit; the nasal, another branch from the same 

 source, emerges above the tendo oculi, and inosculates with 

 the angular branch of the facial artery; the frontal, also 

 from the ophthalmic, appears near the same point, and is 

 distributed to the forehead. 



The LACHRYMAL GLAND is situated in the hollow of the 

 external angular process of the frontal bone, and admits 

 of examination at this time by dividing the upper e3 T elid 

 at its centre and at its external angled It is a thin flat- 

 tened body, the size of a small chestnut, resembling in its 

 structure the salivary glands ; it sends a prolongation down 

 upon the cartilage of the upper eyelid, but its principal 

 portion lies in contact with tlje periosteum, to which it is 

 held by a few fibrous bands ; its inferior surface rests upon 

 the eyeball and the external rectus muscle. It receives a 

 branch of the ophthalmic arter}-. 



To see Homer's muscle, the eyelids must be divided in the middle 

 l>y a transverse cut and turned toward the nose ; the conjunctiva, with 

 the fat and cellular tissue tilling the inner angle of the eye, must be 

 dissected awny. 



The TENSOR TARSI, or HORNER'S MUSCLE, consists of a 

 quadrilateral plane of delicate fibres, closely applied to and 

 arising from the lachrymal bone ; it is about four lines wide 

 and six lines long ; anteriorly it splits into two bands, 

 which terminate in very delicate tendons, to be inserted 

 into each tarsal cartilage by the side of its lachrymal duct. 



