108 SKELETONS OF THE MONOTREMKS, 



Turning to the smaller skeleton of these two Duckbills 

 (No. 2639), it is to be noted that the sternal and costal 

 ribs and the vertebras agree entirely with those of No. 1304, 

 with respect to number and characters. 



In his Osteology of the Mammalia, Flower has quite 

 fully described the vertebrse of the entire spinal column in 

 the Echidna and the Duckbill; and I find that the specimens 

 here under consideration in no way depart from those de- 

 scriptions. In these two specimens of Ornithorhynchus the 

 odontoid process has thoroughly united with its proper ver- 

 tebrae, which is very good evidence that they are well along 

 in life; and notwithstanding the fact that No. 1304 is much 

 the larger of the two, both having highly developed spurs 

 would point toward their both being males. 



The Skull in the Echidna at hand departs in no way 

 from the descriptions of that part of the skeleton as given 

 by Flower, Owen, and other eminent comparative anatomists, 

 and this is also true of the sternum and shoulder girdle. 

 The general outline of an Echidna's skull is well shown here 

 in Figures 10 and 11. It is noted for its very feeble and 

 delicately constructed mandible and the general lack of 

 character of the cranium, which is quite devoid of the usual 

 salient apophyses, marked foss£e, and conspicuous foramina. 



In the Ornithorhynchus the sacrum is of much feebler 

 build than it is in the Echidna, while in both its hinder por- 

 tion makes an acute angle with the chain of caudal verte- 

 brse. All that Owen has to say about this bone is that "the 

 "sacrum consists of tv/o vertebrse in the Ornithorhynch%is, 

 "and of three in Echidna" (p. 317). 



As all three of these skeletons are of adult specimens, 

 it is not possible to decide whether in any of them an os 

 acetabuli is present or not. Flower evidently entertained the 

 opinion that the Monotremata lacked this "fourth pelvic 

 "bone," and says of it in general that "its. morphological 

 "meaning is as yet unknown, but it can scarcely be con.-sid- 

 "ered as an epiphysis." This authority's description of the 

 pelvis in the monotremes agrees with that bone as exemplified 

 in these Army Medical Museum skeletons; he states that "in 

 "the Monotremata the pelvis is short and broad. The ilia 

 "are short, distinctly trihedral and everted above. The 

 "ischia are large, and prolonged into a considerable back- 

 "ward-directed tuberosity. The symphysis is long, and 

 "formed about equally by pubes and ischium. The thyroid 

 "foramen is round. The acetabulum is perforated in Echidna 

 "as in birds, but not in Ornithorhynchus. The pcctinal 



