EYE OF THE ENGLISH SPARROW 365 



covered by the proximal portion of the rectus internus muscle, 

 but the gland overlies the distal third of this muscle. The 

 ventral portion of the gland partly conceals the inferior rectus 

 and the inferior oblique muscles. MacLeod ('80) describes this 

 gland in the duck as a typical tubular gland. 



The blood supply to this gland is from the ophthalmotemporal 

 branch of the external ophthalmic artery and from the ophthal- 

 mic vein (figs. 15 and 17). These, as they pass under the gland 

 to supply the inferior oblique muscle, give off numerous branches 

 to this gland which penetrate its under surface. 



The nerve supply is from the inferior branch of the third 

 nerve, which, as it passes under the gland to supply the inferior 

 oblique muscle, gives off a twig to the under side of the gland 

 which branches and ramifies over its under surface, fine branches 

 penetrating the gland. 



After the gland has narrowed to its duct at the anterior end, 

 it lies under the two oblique muscles. The walls of the duct 

 from this point become much thinner and lose their glandular 

 appearance. The duct passes around the eye, closely adjacent 

 to it, and opens into the anterior lower portion of the conjunc- 

 tival sac under the nictitating membrane. The single opening 

 is rather large and can be easily entered by passing a seeker 

 under the nictitating membrane into this portion of the con- 

 junctival sac (fig. 5, H). The very copious secretion is thus 

 emptied near the region of the most active part of the nictitating 

 membrane. At this point the conjunctival sac is more or less 

 cup-shaped, which allows the accumulation of a considerable 

 amount of fluid. The physiological significance of this is readily 

 seen when we consider the movements of the nictitating mem- 

 brane, previously described. 



A better idea of the arrangement of the structures involved 

 in the cleansing of the front of the eye can be had by consulting 

 the diagram (fig. 7), a horizontal view. The large Harder's 

 gland {Hg), situated back of the eyeball, pours out, by means of 

 its duct {Hd) , a copious secretion at the anterior canthus between 

 the nictitating membrane and the eyeball. There is also a 

 scanty secretion from the lacrimal gland (Lg) which enters at 



