96 PEOF. OWEN ON A CAENIVOEOTJS EEPTILE. 



The lower canines (ib. fig. 5, c', c') had risen, as in Machairodus, 

 immediately in front of the upper ones, and presented the same 

 inferiority of size ; hut they are divided, in Cynodraco, hy a tooth- 

 less interval, or " diastema," from the lower incisors (ib. i, 1, 2, 3, 

 4). In this character, as in the number of incisors, the South- 

 African Karoo fossil resembles the Marsupial genus Didelphis. 

 The lower incisors are suhequal, subcompressed, and elliptical in 

 transverse section, at least at the base of the crown, with the long- 

 axis of the section directed from the fore to the hind part of the 

 alveolar border ; and they are close-set, as in carnivorous mammals. 

 As in these, also, the dentine, in both canines and incisors, is of the 

 hard unvascular kind, and the enamel as distinct in tissue and as thick. 



The decrease in size is from the 1st to the 4th ; but the degree 

 shown in the fossil and fig. 5 may be due to section at different 

 heights from the base. 



Associated with this fossil, or from near the same locality, was a 

 larger oblong block of the same matrix, with the ends of a long 

 bone partially visible. Out of this block an entire humerus was 

 developed (PL XI. figs. 6-9, half nat. size). It is of a left fore limb, in 

 length 10 inches 6 lines, with some loss by abrasion of both articular 

 extremities, the shaft showing well-marked developments for mus- 

 cular attachments and other characters unusual or unknown in the 

 Reptilian class. 



The breadth of the distal end — the extension of strong ridges from 

 both the outer (e, e) and inner (/,/') sides, just above the elbow- 

 joint, indicative of strong supinators, flexors, and extensors of the 

 forearm and paw — the modification of the articular surfaces of that 

 end, better preserved than those above, for the combination of due 

 attachment of two bones of the forearm with freedom of motion, 

 not only in the bending and extending, but in rotating on each 

 other, so that the paw could be turned "prone" and "supine," 

 whereby its application as an instrument for seizing and lacerating 

 is advantaged, — add to this the structure, hitherto known only in 

 the Mammalian class and preeminently in the feline family, of a 

 defence of the main artery and nerve of the forearm from com- 

 pression during the action of the above-named muscles by a strong 

 bridge of bone (li) spanning across them, furthermore the exten- 

 sive and powerful ridge (6, 6') at the proximal half of the humerus 

 for the attachment of arm-muscles, especially the deltoid, — the 

 combination of these characteristics, which Cuvier dwells upon in 

 contrasting the humerus of the feline and bovine mammals *, are 

 here exemplified in a fossil homologue, from a formation of the 

 Triassic or Permian division of geological time. 



Extending, however, the comparison of the present humerus 

 beyond the salient features above defined, the head of the bone (fig. 8) 

 differs from that of the feline humerus in being broader transversely, 

 instead of from before backward ; the articular part is oblong and 

 narrow, not hemispheroid nor nearly so convex ; there is no eleva- 

 tion of an outer transverse tuberosity. The representative of the 



* Ossemens FossnV, vol. i. (4to, 1821) p. xlyii. 



