1910.] The Skeleton of Monotremcs: Archaic Characters. 153 



Scapula. The anterior border of the scapula, as shown by its connection 

 with the clavicle, and by the relations of the muscles, is homologous with the 

 spina scapuli^e and acromion of the other mammals (Wilson and ]McKay, 

 1893, Broom, 1899). The prcspinous fossa is absent {Echidna. ? Secondary), 

 or rudimentary (Ornithorhijnchus. Primitive). The glenoid fossa is trans- 

 versely elongate and is borne by the coracoid (primitive) and scapula, 

 whereas in most mammals it is antero-posteriorly elongate and the coracoid 

 portion is generally reduced (compare, however, certain Edentates, Weber, 

 1904, p. 97, in which the true-coracoid takes a considerable i)art in the 

 glenoid). The procoracoids ("cpicoracoids" Weber) overlap in the median 

 line above the T-shaped interclavicle ("episternum") exactly as in Coty- 

 losaurs and other Permian reptiles. (Primitive.) The T-shaped inter- 

 clavicle is unique in mammals but somewhat doubtfully identified vestiges 

 of it, called "pneclavia" occur in higher Mammals (p. 237). 



Humerus. The humerus resembles that of the mammal-like reptiles 

 (p. 119) in the following points: (1) Proximal and distal ends greatly ex- 

 panded. (Secondary emphasis of a primitive character.) (2) Proximal 

 end with very large tuberosities (c/. Fig. 27, no. 2, p. 437), the head being 

 markedly elongate in the direction of the tuberosities. (Partly primitive.) 

 (3) Smaller ectocondylar or "supinator" crest and enormous entocondylar 

 crest with large entepicondylar foramen. (Partly primitive.) (4) Capitel- 

 lum for radius subglobular. (Primitive, cf. p. 436.) (5) Ulnar trochlea on 

 posterior face of humerus, the proximal portion of the ulna being hidden 

 by the radius in front view. On the front face of the humerus, there is no 

 ulnar trochlea, the articular surface being occupied exclusively by the 

 radius. (Largely primitive.) 



Since all of these characters are true of both Ornithorhijnchus and Echidna 

 (notwithstanding the marked divergence in life habits) and are also found in 

 Sphenodou, Pareiasaurus, and Naosaurus, it seems very probable that they 

 are at least in some measure primitive reptilian characters. 



The nhia is remarkable for the expansion and bifurcation of the distal 

 end of the olecranon (possibly a fossorial character, cf. Chrusochloris). 



The manus and pes are full of marked peculiarities. 



Manns. The scaphoid and lunar are fused at least in adults. (Second- 

 ary.) The magnum of Omithorhynchus (Cuvier, 1825, pi. xiv, fig. 13) is 

 fused at its supero-external angle with the cuneiform. (Aberrant.) The 

 unciform is very shallow. In both genera the trapezium is small and does 

 not suggest serial homology with the metacarpals (cf. p. 442). 



The digits are somewhat more subequal than in most mammals. In 

 Ornithorhi/nchus there is the usual mammalian overlap at the proximal 

 ends of the metacarpals, metacarpal IV overlapping III, III overlapping 



