556 



Mr. W. P. Pycraft on the 



Although this shifting of the external aperture of the ear 

 in relation to the orbit has not been accompanied by such 

 profound structural changes as a superficial comparison of 

 this aperture between, say, a Gannet and a Woodcock (text- 

 fig. 5, A & B) might lead one to expect^ yet^ as a matter of 

 fact^ this shifting is associated with very striking skeletal 

 modifications, and these, as we have already indicated, are 

 mainly confined to the cranium. The disturbing factor is 

 apparently the shortening of the basicranial axis. This 



Text-fig. 5. 



A. Diagrammatic side view of the head of a Gannet, shewing the outline 



of the skull and the position of the external aperture of the ear (E) 

 and eye. 



B. Similar view of the head of a Woodcock, to shew the forward 



position of the ear. 



interpretation was first given by Prof. D'Arcy Thompson in 

 an article in ^ The Field,' Nov. 16, 1907 (vol. 110, p. 887). 

 Therein, however, the extent of the changes in the con- 

 formation of the Woodcock's skull were unduly minimized, 

 for the author sought to shew that, while in a skull such 

 as that of the Guillemot the long axis of the cranium was 

 parallel with that of the upper jaw, in the Woodcock these 

 two axes formed almost a right angle with each other — to 

 be quite precise, about 70° (text-fig. 3). 



Prof. D'Arcy Thompson sought, as we have remarked, to 



