[Q OSTEOLOGY OF PTERANODON. 



associated elements to their original form. The anterior border of the large palatal vacuity 

 is the onty part of the drawing which is conjectural. 



The small curved and natural edge of bone in front of the basisphenoid, which in P. 

 longiceps Professor Marsh supposed to be the posterior limit of a large and simple palatal 

 vacuity, is here shown to be merely the rear border of a small oval foramen occupying 

 in part the position of the small median vacuity of Nyctosaurus, described and figured 

 by Professor Williston {Jour. Geol., 1902) as the interpterygoid vacuity. In front of this 

 extends a remarkable trident-shaped ossification, the slender and pointed median spindle 

 of which is here identified as the parasphenoid. At the base of this element arises on 

 each side a round and tapering rod, which projects diagonally forward and outward 

 across the palatal vacuity, as shown in the figure. After fusing with the palato-pterygoid 

 ribbon, which it overlies, it becomes continuous with the delicate transpalatine. In the 

 fossil skull, the diagonal of the right side is broken close to its origin at the base of 

 the parasphenoid, and the distal portion has been lost ; the diagonal of the left side was 

 broken midway of its length, and owing to the lateral crushing of the specimen the 

 posterior part slightly overlaps its own forward extremity. The pneumatic canals 

 pervading nearly every part of the skull are visible even at the fractures of these 

 slender rods. 



Dr. J. Versluys, Jr., of the University of Giessen, who has examined the type skulls of 

 Pteranodon, has kindly expressed his satisfaction with the plate showing the form of the 

 palatal region of P. ingens, although his views as to the homology of some parts of the 

 skull differ from those of the present writer. Thus Dr. Versluys identifies as "basiptery- 

 goid processes of the basisphenoid " the oblique rods arising at the base of the para- 

 sphenoid ; and accordingly he would apply the name of basioccipital to the ossification 

 in the -base of the skull supposed by the writer to represent the united basioccipital and 

 basisphenoid. 



There is perhaps no more convenient test for the interpretation of any reptilian cranium 

 than the ease with which its homologies may be traced in the extremely generalized 

 skull of Hatteria. The writer is confident, therefore, that when submitted to this test 

 the homologies of Pteranodon as understood by Marsh and Williston will prove generally 

 correct. 



The sclerotic circle is composed of twelve thin plates of bone arranged with over- 

 lapping edges. In Plate III, figure 1, the left orbit of the type is shown as actually 

 preserved. By removing the matrix from the orbit, the circle was exposed, pressed 

 inward against the interorbital septum, the component plates being apparently little dis- 

 placed from their normal position. As these parts are somewhat indistinctly rendered 

 in the photographic plate, they are again shown in Plate V, figure 3. 



Supraoccipital Crest. 

 The supraoccipital crest is better preserved than that of the type of P. longiceps, but 

 here also an indefinite part has been lost. The form of the complete crest is known 

 only from the fragmentary skull No. 2473, represented in Plate II, figure 2. Enough of 

 the base of this cranium remains to show that it is of almost exactly the same size as 

 the type skull No. 2594, and fragments of the wing bones also prove that the skeleton 

 of which it was a part nearly equaled in size the type skeleton of P. ingens, No. 1175. 

 The crest may have been flexible, for in all examples known it is found to be ex- 

 tremely thin, in the type its transverse measurement posterior to the supraoccipital plate 



