[li)l().] " Prcaxiar' and " r'ustaxial" border.^ of the Limbs. 433 



to the evidence of the former large size of the coracoid in Edentates (Weber) 

 and Rodents (Howes) suggests that the scapula of Placentals may have 

 passed through a stage retained in the adult Monotreme. This hypothesis 

 is somewhat strengthened by the great depth of the spina scapulae and the 

 small size of the prespinous fossa in the most primitive Insectivores; for 

 according to the theory mentioned on p. 152, the border of the spine in 

 Placentals and ^larsupials is homologous with the anterior (acromial) border 

 of the scapula in Monotremes, and the prespinous fossa is a neomorph. 

 Since the Placentals and Marsupials are believed to be related and the 

 Marsupials stand on a lower plane with respect to many characters, the occur- 

 rence of a Monotreme stage in the development of the shoulder girdle of 

 Marsupials (p. 157) strengthens the inference that the Marsupio-Placental 

 stem also passed through this stage. Finally, this conclusion is supported 

 by the clear conception of the homologies of the borders and surfaces of the 

 scapida in Prototheria and Theria which was worked out by means of a 

 thorough study of the musculature by Wilson and McKay (1893), and by 

 Broom (1899). Thus the Monotremes, in respect to the shoulder girdle as 

 well as to the reproductive apparatus and functions and many details of the 

 brain and vascular system are morphologicalhj ancestral to the higher mam- 

 mals. 



From all this it follows that the blade of the scapula in the ancestral Mar- 

 supio-Placental (p. 226) Avas not reflected back over the ribs but was held 

 in a nearly vertical position (Broom) ; the glenoid facet also must have been 

 elongate and the head of the humerus flattened, with the shaft of the hu- 

 merus running backward, ))ut perhaps not so sharply outward as it does in 

 Monotremes. This agrees perfectly with the evidence offered by the scapula 

 and humerus of Cynodonts, which also show other ancestral Marsupial 

 characters (pp. 119-120). 



The humerus of the ancestral mammal must furthermore have resembled 

 that of the Cynodonts, i. e., it had very strong crests, a very broad heavy 

 entocondyle ("entepicondyle" Owen), and a very large entepicondylar 

 foramen . 



The radius was very probably antero-internal to the ulna, i. e., with 

 reference to the humerus and partly to the anteroposterior axis of the body. 

 This condition is preserved in Stegocephalia (e. g., Erijops), Cotylosauria 

 (e. g., Labiclosaurus, Pareiasaurus), Pelycosauria (e. g., Naosanriis), Rhyn- 

 chocephalia (r. g., Sphenodon), Monotremata, and to a very large extent 

 in all primitive Marsupials and Placentals. The idea that the jn-oximal 

 end of the ulna originally had a considerable share in the internal anterior 

 face of the humeral trochlea (Flower) apparently is based on the condi- 

 tions in Man and other highly specialized mammals. The flattened internal 



