1890.] On the Anatomy and Development of Apteryx. 457 



preaxial distalia are distinguishable in early stages. The distalia 

 usually concresce with the second and third metacarpals to form a 

 carpo-metacarpus, with which the radiale and ulnare may or may not 

 become united. 



The pollex usually atrophies at an early stage, but a vestige of it 

 may persist. 



The manus is fairly constant in structure in A. australis and A. 

 Oweni, but is very variable in A. Bulleri. 



The Pelvic Girdle. — The pubis and ischium are nearly vertical in 

 stages D and E, and gradually become rotated backwards. 



The post-ilium is already f ally formed in stage D, the pre-ilium not 

 until stage Gr. 



The pectineal process is ossified equally from the ilium and the 

 pubis. 



The Hind-limb. — In the tarsus a tibiale, a fibulare, and a single 

 distale are distinguishable in stages D and E. In F a post-axial 

 centrale appears in the rudiment of the mesotarsal articular pad ; in 

 G it becomes chondrified, and in the adult ossified. A smaller pre- 

 axial centrale is first seen as a distinct chondrite in stage L ; in the 

 adult of A. australis and A. Haasti (?) it was observed as a separate 

 bone in the preaxial moiety of the mesotarsal pad. 



In stage D the fifth digit is represented by an elongated meta- 

 tarsal ; in E this has diminished in size, and in F undergone almost 

 complete atrophy. 



Muscles of the Wing. — The following muscles are present in the 

 wing in addition to those described by Owen : — Brachialis anticus, 

 supinator, pronator, anconeus, flexor profundus internus, extensor 

 carpi ulnaris, extensor metacarpi radialis brevis, extensor indicis 

 proprius, and flexor digitorum profundus. There may also be a 

 brachialis anticus accessorius, an interosseus dorsalis, and probably 

 a flexor carpi radialis. 



The biceps arises from the acrocoracoid, the triceps by a long 

 head from the scapula and by a short head from the humerus. 



The Brain. — The mesencephal is unusually small from the first ; in 

 stages D — P the optic lobes are dorsal; in Gr they become lateral by 

 the transverse extension of the optic commissure or median portion 

 of the roof of the mesoccele ; in H they are already ventral, although 

 larger proportionally than in the adult. 



The diencephal becomes tilted backwards in later stages, its dorsal 

 wall becoming posterior and the foramen of Monro postero-dorsal 

 instead of antero-dorsal. 



The anterior commissure and corpus callosum are large. 



The cerebral hemispheres are of unusual proportional length, and 

 partly cover the cerebellum. 



The Eye. — A pecten is present during late embryonic life. 



