26 OSTEOLOGY OF PTERANODON. 



slightly incomplete. Across the middle of the glenoid surface can be seen the suture 

 between the component elements. Two views, front and rear, are shown of the left 

 scapula and coracoid belonging to the smaller Pteranodon sp., No. 2616 (Plate XVIII, 

 figures 1 and 2). The articular coracoidal facets of the sternum of this individual have 

 been shown in Plate XIV, figure 2. Upon examination, these figures will be found to 

 agree in the main with Professor Williston's admirable description of this part of the 

 shoulder girdle in his paper entitled : " Restoration of Ornithostoma." In the right scap- 

 ula and coracoid of Pteranodon sp., No. 1181 (Plate XXIII, figure 1), a deep and narrow 

 depression lies immediately behind the glenoid surface. It is presumably the coracoidal 

 foramen mentioned by Professor Williston. While no other specimen in the collection 

 shows unmistakable evidence of this foramen, there is no reason for supposing that it 

 was wanting in some of the species. 



The following quotation is from Professor Williston's description of the " Coraco- 

 scapula " : — 



" This bone is stout, U-shaped, with the coracoid arm distinctly longer than the 

 scapular. The distal extremity of the scapula has a large oval facet placed obliquely to 

 the long axis, and evidently also obliquely to the transverse axis of the body, indicating 

 that the bone was directed not only outward and downward, but also more or less for- 

 ward. The shaft in all the known specimens below the articulation is trihedral or flat- 

 tened, but in life it was evidently round or oval in cross-section. On the lower part 

 the width is greater, due to a projection of the dorsal side before the glenoid articulation, 

 for the attachment of muscles. The glenoid articulation is deeply concave from above 

 downward, convex from side to side and bounded both above and below by a prominent 

 ridge, that on the inferior border being much stronger than the upper one. The surface 

 is markedly oblique to the plane of the bone, doubtless in life directed outwardly and 

 posteriori}' in the oblique position of the bone that I have described. The surface is 

 considerably narrower from side to side below than above, and in this direction [side to 

 side] it is convex throughout. A rugose line, indicating the junction of the two bones, 

 passes directly backward near the middle of the articular surface. At the bottom of the 

 U, formed by the conjoined bone, there is a process arising from the scapula and reach- 

 ing to the anterior surface of the coracoid, to which it is joined ; it incloses a small, 

 oval foramen just back of the middle of the glenoid surface. The diameter of the 

 foramen is about twelve millimeters. 



'• The shaft of the coracoid is flattened antero-posteriorly in all the specimens, though 

 probably in life oval. On its proximal half there is a prominent process on the inferior 

 border for muscular attachment. From beyond the middle the sides of the bone are 

 parallel. The sternal articulation is gently concave in one direction and slightly convex 

 in the other, to agree with that of the sternum, forming a reciprocal joint, which must 

 have had considerable mobility. A little above the sternal end, on the posterior side, 

 there is a narrow rugosity, more than an inch in length, for muscular attachment." 



The different skeletal parts comprising the thorax have been described separately and 

 may now be considered in their joint relationship to the act of respiration. The only 

 considerable and essential portion of the thoracic frame remaining in any doubt is the 

 series of sternal ribs. As the writer is not aware that these have ever been positively 

 identified in Pteranodon, it may be well to call attention to a small but seemingly com- 

 plete bone (Plate XVI, figure 4) found with the skeleton of P. ingens (type), No. 1175. 

 While this bone is only 41 mm i n length, its form closely resembles that of some of 



