GLANDS OF THE EYE. 



193 



in Reptiles this becomes more developed in the region of the 

 anterior and posterior angles of the eye, and the original connecting- 

 bridge gradually disappears : thus two glands are developed from 

 the primitively single one, each of which becomes further diffei- 

 entiated both histologically and physiologically. From one is formed 

 the Harderian gland, which always lies at the anterior angle of 

 the eye, surrounding to a greater or less extent the antero-ventral 

 portion of the eyeball, while the other gives rise to the lacryrnal 

 gland (Fig. 157, H, H\ Th). The latter retains throughout life 



FIG. 157. HARDEKIAN GLAND (H, H 1 ) AND LACRYMAL GLAND (Tk) OF Ancjuis 



fragilis. 

 M, muscle of jaw ; B, eyeball. 



FlG. 158. DlAGJRAMMATIC TKANSVI'.li.SE VERTICAL SECTION THROUGH THE EYE OF 



A MAMMAL. 



Op, optic nerve ; B, eyeball ; Fo, Fo, foriiix conjunctiva' : Lff, LH, outer skin 

 of the eyelids, which at the free edges of the latter at t becomes continuous 

 with the conjunctiva ; T, the so-called tarsal fibre-cartilages, in which the 

 Meiboniian glands (ML) lie embedded, the latter opening at * ; H, H, eyelashes. 



its primitive position at the posterior angle of the eye, and in 

 Reptiles and Birds even lies in the region of the lower eyelid, 

 being supplied by the second division of the trigeminal. In 

 Mammals it becomes gradually further subdivided, and extends 

 into the region of the upper eyelid, so that its ducts open above 

 the eye into the upper conjunctival sac (Fig. 159,**). Nevertheless, 

 even in the Primates, more or fewer ducts are present which open 

 into the lower conjunctival sac, and thus the primitive position of 

 the lacrymal gland is indicated. 



o 



