36 



NEW REPTILES AND STEGOCEPHALIANS PROM 



which extend back to the middle of the axis and carry distinct facets for articulation 

 with the anterior zygapophyses of the axis. The lower face of the centrum is broad 

 and flat or even shghtly concave. On the posterior external corners there are small 

 but prominent processes for the capitula of the atlantal ribs; smaller processes, almost 

 destroyed by decay, lie on the sides of the arch near the level of the base of the neural 

 canal. The anterior face is deeply concave below, forming a socket for the nearly 

 spherical occipital condyle. The upper edges of the face are drawn in sharply below 

 the anterior processes and form the sides of the deep notch which receives the anterior 

 end of the odontoid process. The diameter of the neural canal is considerable. 



Fig. 9. — DesmatosuchxLs spurensis. 



A. Upper surface of atlas and axis. B. Anterior surface of same. C. Anterior surface of a 

 second axis, No. 7504, U. of Mich. D. Lateral surface of same. All figures X 0.5. 



The axis is much larger than the atlas, and though the sutures are closed it is 

 evident that the vertebra is composed of the elements suggested by McGregor, an 

 intercentrum and the axis proper. The neural spine is elongate and thin, except at 

 the anterior end, where it is expanded and heavy; this portion lies upon the down- 

 wardly and backwardly sloping arches of the atlas. The anterior zygapophyses are 

 covered, but are of good size, with the faces looking almost directly upward. The 

 posterior zygapophyses are nearly normal in form; they overhang the posterior edge 

 of the centrum for some distance. The lower face of the centrum is flat from side to 

 side and concave antero-posteriorly on the posterior or true axial portion. The process 

 for the capitulum is larger than for the tuberculum and a little in advance of it. The 

 neural canal is still large, but smaller than in the atlas; the transverse diameter is the 

 larger. The posterior face of the centrum is deeply concave. 



A second axis found with the remains of Desmatosuchus, and evidently belonging 

 to an individual of the same genus and species, is even more perfect. In this (fig. 9, 

 c and d) it is seen that the odontoid process is quite broad; the posterior zygapophyses 

 show a peculiarity which is continued backward for some distance in the cervical series; 

 the posterior end of the zygapophyses extends beyond the articular face and on its 

 upper surface there is a decided prominence. 



The next two vertebrae (fig. 10) were found isolated in the matrix of the specimen 

 and are regarded as the third and fourth because of their size and shape. They, are in 

 poor condition, but show the main characters. The neural spine of the third is partly 

 rotted away, but the base of the spine indicates that it was thin laterally and somewhat 

 elongate. It was evidently low. The anterior and posterior zygapophyses are on 

 nearly the same level and are normal in form and position. The transverse process is 

 elongate and extends nearly straight downward, but a little to the rear. The sides of 

 the centrum are concave and the lower end of the transverse process is free for some 



