EYE OF THE ENGLISH SPARROW 



369 



are inserted upon the eyeball a little beyond the equator by a 

 broad, thin, and almost transparent tendons (figs. 11 and 23). 

 The superior rectus (Rs) partially overlies the quadratus and 

 the insertion of the superior oblique. The rectus internus (R in) 

 is partly covered 'by Harder 's gland (Hg) and the superior 

 oblique (Ob s) . The belly of the inferior rectus (R inf) is partly 

 overlapped by Harder's gland. The insertion lies partly under 

 that of the inferior oblique {Ob i). It conceals the pyrainidalis. 



Fig. 10 Enlarged view of a cross-section of the head at the base of the beak 

 about 2 mm. anterior to the eyes to show the lacrimal canals leading to the 

 choana. A-A, right and left air passages connecting the external nares and the 

 buccal cavity, BC, through the choana at P; F, frontal sinus; J, organ of Jacob- 

 son; L, lacrimal ducts opening by horizontal slit-like openings into the choana; 

 the anterior wall of the right duct has been cut away; M, maxillary sinus; T, 

 turbinals. 



The insertion of the rectus externus {R ex) is partly concealed 

 by the lacrimal gland. 



The superior oblique (Ob s) and the inferior oblique {Ob i) 

 have then' origin at about the same place on the nasal side of 

 the orbit, just above the duct from Harder's gland. The superior 

 oblique extends directly from its origin to its insertion on the 

 eyeball near that of the rectus superior. The pull is direct, and 

 is not transmitted through a pulley-like arrangement as in mam- 

 mals. The insertion of the inferior oblique is in the region of 

 that of the rectus inferior which it partly overlies. 



