28 



NATURAL HISTORY OF BIRDS. 



birds. Thfir niimlKT was about forly-niiif, a liiyh nuinbt-r for the class; but the most 

 iiitereatiiig part of the vertebral column is undoubtedly the tail, which was composed 

 of the t;real number of twelve verlebrie. The middle and ]iosterior ones had very 

 long and broad transverse jiroeesses, which re.-itricted lateral motion, clearly indicating 

 that the tail was mainly moved uj) and down, evidently as an aid in diving, the lateral 



motion being confined to the tail as a whole, and ]ierforniod between the foremost 

 vertebra;. The last three or four caudals were firmly fused together, forming a flat 

 jilate, analogous to, but (juite unlike, the jdouglishare bone of modern birds. Thus 

 the tail formed a sort of an oar, similar to a beaver's tail (Fig. 14). 



The shoulder girdle, in its retrograde development, is particularly interesting as 

 showing strong resemblance in many res])ects to that of the existing droma'ognathous 

 birds, especially when we remember that Ifcijitroniifi itself had a palatal structure of 

 a similar type; for not only is the sternum devoid of a keel, but the long axes of the 



adjacent parts of the scapula and 

 coracoid were parallel, or identical, 

 as shown in the accomjianying cut 

 (Fig. 15). The breast bone was 

 thin and weak, with a rounded 

 mesial projection in front, corre- 

 sponding to the manubrium; the 

 posterior margin was quite thin, 

 and had two shallow emarginations. 

 The ribs sliow only little dilTerence 

 fmm those of modern birds, and 

 some of them supported uncinate 

 processes. The clavicles were .se]>- 

 arate, resembling the corrcsjwnd- 

 ing bones in the embryos of some 

 modern forms. The coracoids and 

 the scajiida were (piite small. The wing is rejiresented by the rudimentary humerus 

 alone, the other bones having become atrophied. 



The pelvis, though in its general form resembling that (f Coh/mhus, exhibits many 

 features common to that of reptiles, ami of several dronneognathou-s living birds. 

 Alost interesting, jierhajis, is that the condyloid euj) of the hi|)-joint is closed by bone, 

 except a foramen that )ierforate8 the inner wall, entirely unlike the acet.abulum of 

 other birds, but resembling that of the crocodiles. The three constituents of the i)el- 



Fio. 15. — Scaj>ulat' iuclt ul JJt*ijH:ri*i-nU, reduced. 



