PHYLOGENT OF THE PALtEOGNATHTE AND NEOGNATH^E. 233 



The Pectoral Limb. 



The pectoral limb is in all the flightless Palceognathce a very degenerate structure. 



Perhaps that of Rhea should be regarded as the least degenerate. 



In the JRhea the length of the extended ante-brachium and manus is only very 

 slightly greater than that of the brachium. The length of the manus is greater than 

 the ante-brachium. The length of the pollex with its claw is very nearly as great as 

 the ii. metacarpal. In a nestling Rhea I find on the in. digit a vestige of a claw ; a 

 similar vestige has been already detected by Wray in the Ostrich. The ulnare 

 possesses the typical Neognathine form — in Struthio this is a mere nodule. The 1st 

 phalanx of the second digit is broad and flat, the 2nd phalanx is pointed. 



The ante-brachium is about one-third shorter than the brachium. The post-axial 

 border of the ulna from the olecranon outwards for some considerable distance is 

 greatly compressed. The superficial appearance of the forearm resembles that of 

 many long-winged Neognathce. 



In the humerus the pectoral crest is obsolete, as also is the crista inferior. 

 is no subtrochanteric fossa, and the fossa for the brachialis internus is only faintly 

 indicated. 



In Struthio the length of the extended ante-brachium and manus is about one-third 

 less than the length of the humerus, and falls far short of that of Rhea, being but a 

 little more than two-thirds as long as the brachium. 



In Struthio the manus is longer than the forearm, in Rhea the reverse is the case. 

 In Rhea the forearm is about two-thirds and in Struthio about one-third the length of 

 the humerus. The distal carpal mass only just reaches the base of the 1st metacarpal ; 

 in Rhea it extends pre-axiad so as to support the whole base of the pollex. The 1st 

 phalanx of the n. digit is relatively longer in Struthio than in Rhea. The n. metacarpal 

 in Struthio is more or less rod-shaped, that of the in. is rod-shaped and bowed. In 

 Rhea the distal end of metacarpal n. is flabellate, the in. metacarpal is very slender, 

 rod-shaped, and sigmoidally curved. 



The ulna, in Struthio, is much expanded distally by a more or less triangular out- 

 growth of its pre-axial border. The olecranon is but feebly developed. The distal 

 end of the radius is grooved and much expanded in the direction of its articular surface 

 for the radiale. 



The pectoral crest of the humerus is more conspicuous than in Rhea, forming a long, 

 low, swollen ridge. There is a wide and shallow fossa distad of the caput humeri, 

 possibly representing the sulcus transversus. There is also a shallow incisura capitis. 

 The crista inferior is wanting. The subtrochanteric fossa is present but shallow, but 

 it receives no pneumatic apertures. The tuberculum medius is moderately well 

 developed. 



The linea aspera for the triceps is raised into a long and sharp ridge, which reaches 



