252 



ANIMAL PHYSIOLOGY. 



corner or canthus of the eye by a little tendon (tendo oculi) 

 to the bone; and to the sides of this tendon are attached the 

 fibres of the orbicularis palpebrarum muscle, a thin sheet of 

 subcutaneous fibres which pass in circles round the eyelids, 

 spreading over the adjacent parts of the cheek and forehead. 

 This is the muscle by which the eyelids are closed; and its 

 attachment to the tendo oculi explains why it is that, when 

 the lids are forcibly shut, as, for example, by a reflex action 

 on tasting something sour, their edges are drawn inwards to 

 the nose. When the eyes are opened, the lower lid falls back 

 into its place by elasticity, but the upper lid is raised by its 

 levator palpebrce muscle, which comes forward from the back 

 of the orbit, lying on the superior rectus, and is attached to 

 the upper border of the superior tarsal cartilage. On evert- 

 ing either eyelid, a set of nodulated yellow streaks may be 

 seen beneath the mucous membrane or conjunctiva (p. 229). 

 They are the Me ibomian follicles, and are a set of sebaceous 

 glands which keep the margins of the lids oiled, and so help 

 to prevent the tears from running over the cheeks. 



Fig. 125. LACHRYMAL APPARATUS, a, Levator palpebrae muscle; 

 &, tarsal cartilage of the upper eyelid; c, Meibomian follicles, 

 exhibited by division of the upper eyelid and reflection of the 

 outer part ; d, caruncula ; e, plica semilunaris ; /, lachrymal gland 

 with the orifices of its ducts below it; #, canaliculi, with the 

 pimcta lachrymalia on the edges of the eyelids; h, lachrymal 

 sac ; , nasal duct. 



