THE UPPER TRIASSIC OF WESTERN TEXAS. 35 



dilia in almost the same place. The otic cavities were injured in fossilization both by ptessure 

 and by the crystallization of the gypsum and pyrite which filled the cavities of the skull. It is 

 apparent that there was a thin wall between the otic cavity and the brain cavity, but this has 

 been so injured that it is impossible to determine the original form of the otic cavity or the form 

 and position of the semicircular canals. 



"Below are the large cylindrical projections which filled large foramina carrying the IX, X, 

 and XI nerves and the jugular vein. All of these must have escaped through a common opening, 

 as the walls of the brain-case are very perfect in this place and no other openings are present. 



"Near the posterior end of the cast are slender processes which mark the position of the XII 

 nerves. Above these processes there are small prominences which filled pits in the inner walls of 

 the exoccipital bones. These pits were entirely cleared, and it is certain that they were not the 

 beginnings of foramina, their meaning is unknown. 



' ' The whole metencephalic portion of the cast is rather high and narrow. It is possible that 

 this is due in some degree to crushing, but there is no indication of such crushing in the skull, and it 

 is probable that it is the true form. The whole cast is very small relative to the size of the animal, 

 and even assuming that the brain occupied the whole cavity its size would be remarkable, though 

 after all it is not much smaller, relatively, than the brain of Sphenodon or of an alligator. 



" It is difficult to make any satisfactory comparison of this endocranial cast with the one made 

 by Cope from the specimen of Belodon buceros because of the unsatisfactory nature of his figures, 

 but some points can be made out. As can be seen by the figures in his paper, the whole shape is 

 different, the cast from Belodon does not show the sharp downward curve posterior to the middle 

 region. The cast of Desmatosuchus is thinner for its height and does not have so long a meten- 

 cephalic portion. 



"The epiphysis lacks the posterior prolongation, certainly it is not ' subquadrate ' in form, 

 and the lateral processes rise in front of, not at the sides of, the epiphysis. The olfactory tracts 

 were much broader. The optic nerves did not escape through distinct foramina. Only the origin 

 of the pituitary body is shown in Cope's figures, but he describes it as small and occupying a fossa 

 in the base of the cranial cavity. These characters support the evidence afforded by the bones of 

 the skull that Desmatosuchus must be placed, at least, in a distinct suborder from the Phytosauria." 



The vertebral column (see plates 6 to 10). — The exact number of presacral vertebrae 

 has never been determined in the Phytosauria. McGregor says that it is "practically 

 certain that there were not less than 25 or more than 27" in the presacral series. In 

 the mount and restoration of Desmatosuchus, 28 vertebrae have been included in the 

 presacral series; while this number may not be exactly correct, every consideration 

 of the condition of the specimen and the character of the vertebrae indicates this 

 number; of all the material found, three cervicals, which are obviously duplicates, and 

 one dorsal have been excluded in making the mount. It is possible that the single 

 dorsal should have been included, but it is apparently a duplicate and its inclusion 

 would have made the presacral series seem unduly long. This restoration is subject to 

 correction by future discoveries. 



The atlas and axis (fig. 9 A to d).— The first two vertebrae are closely united but 

 not coossified. The shape of the two is very similar to that figured by McGregori 

 for Mystriosuchus. The atlantal ring is complete, with but slight rugosities indicating 

 the position of the suture between the intercentrum and the neural arch. The arch is 

 completed above by a thin plate which passes obliquely backward beneath the anterior 

 end of the neural spine of the axis. On either side the centrum bears projections from 

 the anterior edge near the lower level of the neural canal; these are marked off by a deep 

 notch below and project sharply from the anterior edge of the neural arch above. The 

 one on the right side is smooth, as if there were an articulation for a proatlas. This 

 may be deceptive, however, as the corresponding projection of the other side does not 

 have this appeara nce. There are strong projections from the rear of the neural arch 



1 McGregor, J. H., American Museum Natural History, Memoir ix, pt. ii, p. 62. 



