458 On the Anatomy and Development of Apteryx. [Apr. 17, 



Phylogeny. — The following characters support the view that 

 Apteryx is derived from a typical avian form capable of flight : — 



(a.) The presence of an alar membrane or patagium. 

 (6.) The presence of pterylae and apteria. 

 (c.) The presence of remiges and of tectrices majores. 

 (d.) The attitude assumed during sleep. 



(e.) The presence of two articular facets on the head of the 



quadrate. 

 {/.) The presence of a pygostyle. 



(g.) The extreme variability of the sternum, shoulder girdle, and 



wing, indicating degeneration. 

 (h.) The occasional occurrence of a median longitudinal ridge or 



vestigial keel on the sternum, 

 (i.) The position of the shoulder girdle and sternum in stage E. 

 (j.) The presence of vestigial acromial, procoracoid, and acro- 



coracoid processes. 

 (&.) The fact that the skeleton of the fore-limb is that of a true 



wing in stage F. 



(7.) The early assumption of undoubted avian characters in ihe 

 pelvis. 



(m.) The typically avian characters, both as to structure and deve- 

 lopment, of the vertebral column and hind-limb. 



(n.) The fact that the brain passes through a typical avian stage 

 with lateral optic lobes. 



(o.) The relations of the subclavian muscle. 



On the other hand, the total absence of rectrices tells against this 

 view. 



The following characters indicate derivation from a more general- 

 ised type than existing birds : — ■ 



(a.) The characters of the chondrocranium, especially in the 

 earlier stages. Many of these peculiarities, e.g., the absence 

 of an interorbital septum, may, however, be adaptive, and 

 correlated with the diminished eyes and the enlarged olfac- 

 tory organs. 



(6.) The presence of an operculum in early stages. As, however, 

 this structure has not been described in Reptiles, it either 

 proves nothing or too much. 



(c.) The presence of a well-marked procoracoid in comparatively 

 late embryonic life. 



(d.) The characters of the pelvis. 



On the other hand, in the following characters, Apteryx exhibits 

 greater specialisation than other birds : — 



