CERVICAL VERTEBRAE OF PTERANODON. 15 



CERVICAL VERTEBRAE OF PTERANODON. 



The cervical vertebrae are nine in number, counting the elementary atlas and axis as 

 the first two units of the column. This is proved beyond all doubt by comparing the 

 cervical series in the type of P. ingens, No. 1175 (Plate VI, figures 1-6), which consists 

 of the seven anterior vertebrae, with the parts preserved of the cervical series of a 

 smaller example of Pteranodon sp., No. 2692 (Plate VI, figures 7-9), in which the com- 

 plete seventh, eighth, and ninth vertebrae remain in their natural sequence. Both these 

 series have been slightly restored by the artist. In all examples of the genus found in 

 the collection, the atlas and axis are coossified, and neither in the small type of P. longi- 

 ceps, No. 1177 (Plate VI, figure 11), nor in the much larger P. ingens, No. 1175 (Plate VI, 

 figures 1 and 12), is it possible to trace readily the limits of the elements theoretically 

 composing these united vertebrae. As the atlas and axis of P. longiceps have been 

 crushed transversely, while the same parts of P. ingens have been subjected to pressure in 

 the axial direction only, the true form of these bones may be more easily understood 

 by a comparison of the two figures mentioned. Viewed laterally, these vertebrae have 

 much the same appearance as the corresponding parts of Nyctosaurus, figured by Pro- 

 fessor Williston (On the Osteology of Nyctosaurus). Above the neural arch, which is pro- 

 portionately smaller than in Nyctosaurus, the thin spine extends upward and backward 

 in an easy curve. At its mid-height, the wide-spreading postzygapophyses are given off. 

 The sides of the axial centrum are excavated deeply, thus materially lessening the 

 weight. In the types of P. ingens* Nos. 2594 and 1175, pneumatic foramina may be seen 

 leading forward and backward from the lateral excavations. In the posterior view, the 

 convex oval termination of the centrum appears more produced transversely than that 

 of Nyctosaurus, and the supplementary articulating processes, termed by Professor Willis- 

 ton the exapophyses, are not confluent, but remain separate and distinct as in the 

 other cervicals. That these vertebrae, in spite of their apparently massive form, were 

 extremely light, is also indicated by the paired fenestrae seen on the posterior wall of 

 the arch, a little above the level of the neural canal. The delicate cancellous structure 

 disclosed within may have been occupied by the pneumatic cells that seem to have 

 pervaded nearly all parts of the skeleton in this genus. 



The third, fourth, fifth, sixth, and seventh cervicals are alike in general form, and the 

 slight differences which they offer lie in their comparative lengths. There can be no 

 serious doubt as to the natural sequence of these vertebrae, for in P. ingens, No. 1175, 

 they were preserved in so close juxtaposition as to lead to the conclusion that they 

 had been but little disturbed before being covered by the chalk matrix. The measured 

 lengths of the cervical centra of this example are as follows : Third, 61 mm ; fourth, 

 67mm; fifth, 83mm; sixth, 76 mm ; seventh, 65mm. From this it would appear that of 

 these five vertebrae, the third cervical was the shortest, the fourth and fifth successively 

 increasing in length, and the sixth and seventh again becoming shorter, the length of 

 the seventh being reduced nearly to that of the fourth. This sequence is substantiated 

 in part by P. ingens, No. 2594, where the length of the third cervical is but little greater 

 than that of the united atlas and axis to which it remains attached. The fourth ver- 

 tebra of No. 1175, anterior and posterior views of which are shown in Plate VI, figures 

 13 and 14, is very similar to the other long cervicals, and has been already described 

 by Professor Williston (Restoration of Ornithostoma) as follows : - 

 MEMOIRS CONN. ACAD., Vol. II 



