HISTOEY OF THE KIWI. 7 



may remain distinct. All these facts seem to indicate that the fore- 

 limb of Apteryx has passed through a stage in which it was a true 

 wing. 



The sternum or breast-bone of ordinary birds is a large keeled 

 bone, placed almost horizontally : that of the Kiwi is flat and has a 

 vertical position. In a young embryo, however, the cartilage from 

 which the breast-bone arises is almost horizontal, and in three adult 

 specimens I have found a low median ridge, obviously the vestige of 

 a keel. 



In Carinatre the coracoid takes an oblique position while in 

 Apteryx it is vertical : in an embryo shortly before the appearance 

 of the feathers the coracoid is obliquely placed, the vertical position 

 being gradually assumed at the same time as that of the sternum. 



Moreover there are distinct vestiges even in the adult of the 

 acromion, acrocoracoid, and procoracoid processes, and the coraco- 

 scapular angle sometimes sinks as low as 122°, although it may rise 

 to 150°. As in some of the Carinatrc this angle is as much as 106°, 

 the gap between the two groups becomes comparatively slight. 



Further evidence in the same direction is furnished by the 

 muscles of flight. The elevator of the wing (subclavius) arises from 

 the coracoid and passes over the acrocoracoid process to reach the 

 dorsal aspect of the humerus exactly as in Carinata\ 



The most characteristic feature in the brain of birds is the 

 position of the optic lobes which lie, not on the dorsal surface as in 

 other Vertebrata, but one on each side. In Apteryx, in accordance 

 with the small size of the eyes, the optic lobes are greatly reduced 

 in size and are situated on the base of the brain. It is interesting to 

 find that in young embryos these lobes are situated on the upper 

 surface and in close contact with one another, exactly as in a reptile : 

 at about the time when the feathers appear they separate from one 

 another and pass one to each side of the brain, precisely as in 

 ordinary birds : finally as the end of incubation is approached they 

 diminish immensely in proportional size and come to lie on the under 

 surface. 



It has been mentioned that the Kiwi is the only bird in which 

 the eye is devoid of a pecten. This peculiarity only applies in 

 strictness to the adult : in advanced embryos a small but distinct 

 pecten is present. 



The vertebral column and the hind limb of Apteryx are those of 

 a perfectly typical bird — more typical indeed than those of many 

 Carinata>, for instance the Penguins. The pelvis is also strictly avian 

 although simpler than that of most birds. 



So far, then, the structure and development of Apteryx seem to 

 indicate that the ancestors of this extraordinary member of the class 

 were typical flying birds, having interrupted plumage, a keeled 

 sternum placed horizontally, a shoulder girdle of the usual avian 



