SHOULDER GIRDLE. 25 



sternum of a large animal, Pteranodon sp., No. 2546. Through comparison of other 

 skeletal parts, this individual is known to be about nine-tenths the size of the type of 

 P. ingens, No. 1175. Its specific identity, however^ remains doubtful, as no skeletal parts 

 of taxonomic value have been preserved. The inner or upper surface of the anterior 

 portion of another sternum of slightly smaller size, No. 2616, is shown in Plate XIV, 

 figure 2, while figures 1 and 2 of Plate XV are taken from the right and left sides, 

 respectively, of a laterally crushed sternum, No. 2692. This last example is especially 

 useful in giving an idea of the natural shape of the bone, which must presumably have 

 been intermediate between the forms of those crushed vertically and those crushed laterally. 



The nearly complete restoration of the sternum, No. 2546, shown in Plate XVI, figure 5, 

 has been obtained mainly by replacing missing portions of one side by the correspond- 

 ing portions preserved on the other side. The form of the manubrium has been 

 determined partly from the impression left upon the matrix by the portion lost by the 

 collector, and partly by recourse to the sternum of No. 2692. The four lateral articular 

 projections described and figured by Professor Williston, and supposed by the present 

 writer to be for the attachment of sternal ribs, are well shown both in this drawing and 

 in the photographic view (Plate XIV, figure 1). There is also a fifth pair of projections 

 that appear to be for articulation with a fifth pair of sternal ribs. A small round vacuity 

 is seen in the midline close to the posterior border of the sternum. (This has been 

 also observed in another specimen in the Marsh Collection.) Immediately in the rear 

 of this vacuity is a pair of closely approximated articular projections, which probably 

 served to connect with the abdominal ribs. There seems to have been another pair of 

 articulations separated from the median pair by shallow emarginations, as shown in the 

 restored figure, but the frail and imperfect margin of the bone here permits of no definite 

 conclusions. On the right side of the sternum (the left in the figure) a small oblong 

 ossicle lies in each of the first two shallow emarginations. Only one of these ossicles 

 remains on the left side. Their significance is not understood by the writer. 



The manubrium is evidently much deeper in the vertical direction than wide, and its 

 sharp inferior edge is continued backward to the middle of the broad part of the sternum 

 as a rudimentary keel. This is also the condition in the laterally crushed sternum of 

 No. 2692, but in another example that has been subjected to great vertical pressure, as 

 evidenced by the almost total obliteration of the coracoidal facets, no trace of the keel 

 is to be seen. While it is not desired to convey the idea that Pteranodon's sternum 

 bore a prominent keel for the attachment of the pectoral muscles, it would be equally 

 erroneous to describe it as strictly of the ratite type. 



The lateral halves of the broad and thin body of the sternum appear to have been of 

 rounded form, so that this part of the bone may have resembled a shallow dish or trough, 

 with the addition of the low keel-like process on the anterior portion. In the restored 

 figure, the transverse measurement is of course somewhat reduced through foreshortening. 



A posterior view of the right scapula and coracoid of P. ingens (type), No. 1175, is 

 shown in Plate XVII, figure 1. The two united bones are defective behind and below 

 the glenoid, and in order to assemble the fragments it has been necessary to replace 

 the missing portions with plaster of Paris. The general outline will be found fairly 

 correct, but no attempt has been made to restore the bone in detail. In size, this speci- 

 men exceeds all other examples preserved in the Marsh Collection. In the left scapula 

 and coracoid of Pteranodon sp., No. 2512, a posterior view of which is shown in Plate 

 XVII, figure 2, the general proportions are admirably preserved, although the bones are 



