BIRDS 



423 



Figs. 531 and 532. — The Mechanism of the Nictitating Membrane in 



Birds. 



Fig. 531. — The anterior aspect of the 

 ej^e of the turkey. 



Showing the insertion of the pyra- 

 midalis tendon into the nictitans 

 (Bland-Sutton). 



Fi( 



532. — The posterior aspect of the 

 eye of the turkey. 



Showing the pyramidalis 

 fontinued as a tendon (below 

 through the sling formed 

 quadrat us muscle (above) 

 Sutton). 



muscle 

 looping 

 by the 

 (Bland- 



septal system ; a single large septum ma}' run to the axis where it 

 subdivides ; the oligodendroglial cells are widely scattered and 

 numerous, being thickly packed between the fascicules of nerve fibres 

 (Prince, 1955). The decussation of fibres at the chiasma is complete 

 with an elaborate interdigitation of fasciculi (Beauregard, 1875 ; 

 Gudden, 1879 ; Gallerani. 1888 ; Faravelh and Fasola. 1889) (Fig. 529). 



THE OCULAR ADXEXA. The Hfls almost cover the globe revealing 

 only the small cornea through their (usually) circular aperture, 

 deceptively hiding the relatively enormous eye (Fig. 530). In the 





y 



Fig. 533. — The Orbits of the Sparrowhawk, A'cipiTEit. 



