EYE OF THE ENGLISH SPARROW 



403 



for about one-third of their width. This overlapping is regular 

 and shingle-like in arrangement. The combined thickness of 

 the overlapping portions about equals the thickest portion of 

 the plate. A ring of bone of practically uniform thickness is 

 thus formed, completely surrounding the eye. A B oi figure 31 

 shows three, of these bones in their normal position, and illus- 



Fig. 31. Camera outline drawings of the scleral plates, showing how much 

 they overlap and their variation in size. A is from the anterior or nasal side of 

 the scleral ring; B from near the dorsal part; C is a single plate. D represents a 

 section at right angles to A-B. Ant, anterior margin; Pst, posterior margin. 



trates the extent to which they overlap. It also shows that there 

 is a small portion at the posterior end of each plate which does 

 not overlap. In figure 32, a free-hand drawing of an equatorial 

 section through this region, the scleral plates {Scl p) are shown 

 in their relation to the other structures. 



Sections in an anteriposterior direction show the bones almost 

 uniform in thickness and ending bluntly at the two ends. This 



