MORPHOLOGICAL REVISION 87 



including the opisthotic, which unites with the skull above, most extensively 

 with the parietals. Between the outer processes of the exoccipitals and the 

 supraoccipitals above are two small openings, which probably admitted blood 

 vessels to the brain cavity. Near the condyle there is a foramen for the 

 vagus nerve. 



The pterygoids are broad posteriorly, articulating with the parasphen- 

 oid and exoccipitals; the broad posterior portion separates the palatal vacui- 

 ties from the otic notches behind. The outer end divides into two parts, 

 one of which extends backward to the quadrate and borders a deep pit 

 behind. The other extends forward on the outer side of the palatal vacuities 

 and probably unites with the palatines and vomers anteriorly. The sutures 

 can not be made out. 



The ectopterygoid is a distinct element separated from the pterygoid, 

 palatine, and maxillary by sutures. 



There are four vacuities or cavities on the lower surface: the internal 

 nares, far forward, surrounded by the vomers, the palatines, and the maxil- 

 laries; the large, palatal vacuities surrounded by the vomers, palatines, 

 pterygoids, and parasphenoid; the cavity for the coronoid process of the 

 lower jaw, bordered on the outer side by the quadratojugal and on the inner 

 side by the pterygoid; two deep pits, posterior to the pterygoids, excavated 

 in the bones of the horns, which may have sheltered external gills. 



The lower jaw is slender and short, not over one-fourth or one-fifth of 

 the length of the skull. The two halves are coossified at the symphysis; 

 it is impossible to make out the component elements of each ramus. The 

 outer surface is marked by a sculpture similar to that on the skull. There 

 is a single row of teeth except at the anterior end, where there are two rows. 



Vertebral column: There are more than twenty vertebrae in the column. 

 Specimen No. 4472 Am. Mus. Nat. Hist, has nineteen consecutive vertebrae 

 extending from the first to an anterior caudal. No. 652 University of Chi- 

 cago has twenty vertebrae, "mostly continuous." It is probable that there 

 were more than this, perhaps as many as thirty. All the vertebrae are marked 

 on the sides and lower surface of the centrum by a most intricate and deli- 

 cate sculpture of fine, interlacing lines (see plate i). In the caudal vertebrae 

 this sculpture is present on the neural arches and the haemal processes, but 

 is coarser and more rugose. In the series preserved at the American Museum 

 the vertebrae show a gradual increase in both length and breadth to the 

 ninth or tenth, from which point they gradually become more slender. 



The first vertebra, commonly called the atlas, is longer than the second 

 and of a somewhat pentagonal outline. At the anterior angle is a tube-like 

 projection from the edges of the neural canal, which fits into the foramen 

 magnum. The faces for the occipital condyles are elongate oval, and look 

 outward and slightly upward. The neural spine is very broad and low. It 

 bifurcates posteriorly, sending back processes which reach nearly across the 

 second vertebra and embrace its spine. A small process on the anterior end 

 of the spine of the second vertebra fits into a notch at the point of bifur- 

 cation of the first spine. The posterior zygapophyses are well developed 

 and between them is a strong zygantrum. On the lower surface is a broad 

 keel which is reduced in size anteriorly until it disappears near the anterior 

 end. There is no evidence of ribs attached to the first vertebra. 



The second vertebra (axis?) is quite short and fits very closely against 

 the first. The low neural spine has a deep pit, such as occurs in all the dorsal 



