518 



the humerus of the Kangaroo (Plate LXIX. fig. l,f, g) than in that of the Wombat. 

 From the lower and outer part of the ectotuberosity extends the process j\ called 

 "deltoid" in the description of the Wombat's arm-bone {ante, p. 362); and in the 

 prominence and angular form of this process Nototherium resembles Phascolotherinm 

 latifrons more than it does Phase, platyrhinus. 



The low, rough process (d, Plate CXXVII.), answering to that which in the Wombats 

 gives attachment to the common tendon of the teres major and short triceps muscles, 

 is as prominent as in Phascolomys latifrons, but is relatively less and better defined. 

 The smooth thenal surface of the shaft continued down between e' & d is uninterrupted 

 by any oblique ridge or rising, continued, as in Phascolomys, from the process e' to the 

 bridge k, completing the entepicondylar canal. The bridge is relatively broader than 

 in Phascolomys latifrons (Plate CI. fig. 1, k), in which species it is broader than in 

 Phase, platyrhinus (ib. fig. 3, k). The entepicondyle (Plate CXXVII. i) is more pro- 

 duced and better defined than in Phascolomys. The same may be said of the supinator 

 ridge (//, h'). There is no definite coronal depression answering to p in Plate CI. 

 figs. 1 & 3 ; in its absence Nototherium resembles Macropus. There is as little definite 

 evidence of an anconal depression, and the bone is thick where it is either diaphanous 

 or perforated in Phascolomys. The anconal surface of the proximal half of the shaft is 

 not traversed or divided by any longitudinal rising ; but a sharp and well-defined ridge 

 (Plate CXXVII. fig. 2, n), probably giving origin to a portion of the triceps muscle, 

 differentiates, if it be constant, the Nototherian humerus from that of either the 

 Wombats or Kangaroos. Near this ridge is the orifice (ib. ib. r) of the medullarterial 

 canal. There is a depressed and tuberous tract (ib. fig. 2, s) on the anconal surface, 

 above the entepicondyle, which is not present in the recent phytiphagous Marsupials. 

 The ridge bounding the ulnar side of the ulnar articular surface (to) is better defined, 

 and extends further upon the anconal surface than in Phascolomys ; there is a closer 

 approach in Nototherium to Macropus in this particular. The radial convexity (I) is 

 relatively smaller and the ulnar surface (m) is less convex than in either Phascolomys 

 or Macropus. 



The humerus of Nototherium, at first glance, recalled by its robust proportions and 

 strongly developed muscular ridges and processes that of Mylodon robustus. But on 

 comparison the marsupial type of the former was as clearly indicated as the edentate 

 type of the latter. In Mylodon robustus the articular head of the bone is flanked by 

 nearly equal ento- and ecto-tuberosities, neither of which rise above it. The deltoidal 

 tract is low, broad, and long, extending over the proximal two thirds of the shaft, and 

 having its distal, radial border chiefly prominent, and defining there the wide and 

 deep " musculo-spiral " groove. In Nototherium it would seem as if the homologue of 

 this deltoidal ridge bifurcated as it descended, to terminate in the two distinct processes 

 e 1 8c f (Plate CXXVII. fig. 1), the latter of which had the relation to the "musculo- 

 spiral " channel which the undivided deltoidal tract holds in Mylodon. There is no 

 entepicondylar canal in Mylodon ; but it may be remembered that this is present in the 



