Recently published Ornithological Works. 175 



closed for several days. There is no evidence tliat any- 

 organic union occurs between the lid-raargins in these 

 ' born-blind ' birds. In all probability the closed eyes are 

 due to tonic contraction of the .orbicularis muscle as a 

 light-reflex act." 



It follows that, if this is so, we have no means of fore- 

 telling by an examination of the eyelids of the embryo, 

 whether or no such an embryo will be hatched " blind.'' 

 It is probably tj-ue to say that most ornithologists would 

 have thought otherwise. 



Details are given of the structure and functions of the 

 nictitating membrane. 



Slonaker and Wood conclude that this membrane is a 

 conjunctival duplication — a thin translucent membrane 

 composed of delicate connective tissue interspersed with 

 elastic fibres running in various directions. It has a firm 

 thickened free margin, but no hyaline cartilage cells. This 

 latter provision enables the free border to be closely applied 

 to the cornea, so that when it sweeps over the latter it 

 carries with it some of the fluid secretion of the Harderian 

 gland and thoroughly cleans and moistens the corneal 

 surface. The presence of elastic fibres gives to the third 

 lid the qualities of a thin rubber band which, when put 

 upon the stretch, instantly flies back the moment the 

 traction or " pull '■* is released. 



In connection with this nictitating membrane, the impor- 

 tant and interesting structure known as Slonaker's marginal 

 plait is described and illustrated, and the author calls 

 attention to the fact that strangely enough Fumagalli 

 ('' Ueber die feinere Anatomie des dritten Augenlides," 

 Internat. Monatsschr, fiir Anatomie und Physiologie, vol. 

 xvi. 1899, p. 129) seems to have entirely overlooked it. 



Interesting details are given as to the mode of attachment 

 of the Pyramidalis muscle to the free border of the third 

 lid and its mode of action. 



The musculature of the eyeball and the structure of the 

 lachrymal gland and its ducts are described at length. 



