20 OSTEOLOGY OF PTERANODON. 



unfettered by ossified tendons and ligaments. On the other hand, the Gallinaceous 

 birds, a group incapable of long-sustained flight, have the anterior dorsal vertebrae rigidly 

 connected by the coossification of the dorsal spines and of the transverse processes, 

 the hypapophyses also being more or less united in the same manner. 



Drawings have been made of the dorsal and sacral vertebrae of three representative 

 adult birds, and the writer has attempted to identify the points of attachment of the 

 muscles of the trunk by comparison with the excellent figures and definitions given by 

 Dr. Shufeldt in "The Myology of the Raven." Figure 1, Plate IX, is taken from a 

 skeleton of the Burgomaster Gull, Larus glaucus (Y. U. Osteol. Coll., No. 2290). The 

 squarely truncate summits of the dorsal spines are made to appear bifurcated behind 

 by the tendons of origin of the longissimus dorsi, which lie close against the spines 

 of the succeeding vertebras. Underneath these and hidden by them are other paired 

 tendons, which are directed forward from the summits of the dorsal spines and which 

 presumably afford insertion for the same muscle. Extending forward and backward from 

 the ends of the transverse processes are tendons serving as further points of attachment 

 for the longissimus dorsi and for the sacro-lumbalis. Plate IX, figure 2, shows the 

 dorsum of the Coot or Scoter, Oidemia nigra (Y. U. Osteol. Coll., No. 429), in which 

 the tendons arising from the dorsal spines are less developed than those of the previous 

 example, while the tendons of muscles attached to the transverse processes have ex- 

 panded into broad sheets binding the dorsal vertebrae firmly together in an almost in- 

 flexible column. In the dorsum of the Wild Turkey, Meleagris gallipavo (Y. U. Osteol. 

 Coll., No. 360), the vertebral coalescence has reached its highest development (Plate IX, 

 figure 3). The centra of four vertebrse are fused into one continuous mass, and their 

 dorsal spines with the attached tendons are represented by a thin median plate of bone. 

 Lateral flexion of this region is rendered equally impossible by the paired ossifications 

 resulting from the fusion of tendons attached to the transverse processes. Since this 

 consolidation of the dorsal vertebrae in birds, though usually associated with increased 

 power of flight, is not brought about by ossification of the tendons of any muscles 

 of the fore limb, but rather by the ossification of the tendinous origins and insertions 

 of muscles of trunk and neck, it seems possible that the extent to which such 

 development is carried may depend in some slight degree upon the physiology of 

 the cervical region. Should this prove to be the case, there will be less difficulty 

 in accounting for the marked variations of this structure in closely related groups of 

 birds. 



Comparing the figures of the notarium of Pteranodon with that of Meleagris just 

 described, it will be seen that, with the exception of the presence in the pterodactyl of 

 a supraneural plate with oval facets for the scapulae, these two animals have developed 

 similar and equivalent structures ; and, considering the general similarity of avian and 

 reptilian musculature, there can remain little doubt that Pteranodon acquired its remark- 

 able notarium by the same developmental process that may be traced in birds. 



It is interesting to note that while in most birds the coalesced anterior dorsals 

 are more or less rigidly connected with the posterior dorsals underlying the blades of 

 the ilia, in Meleagris a free dorsal intervenes between the sacral or pelvic series and 

 the anterior group, indicating slight flexibility in the same part of the vertebral column 

 where in Pteranodon the writer supposes three or four free vertebrae to have persisted. 



