MORPHOLOGICAL REVISION 



95 



The palatines are short and narrow, reaching from the point of union 

 of the pterygoids and maxillaries about half-way to the internal nares. Near 

 the anterior end is an elevated area with raised rim, supporting a pair of 

 tusks similar to those on the maxillary. 



The prevomers are large plates, reaching from the posterior edge of the 

 premaxillary to a point well back of the internal nares. The union with the 

 parasphenoidis not shown, but it is apparent from other specimens that the 

 latter ended in a sharp point anteriorly. On each bone, near the anterior 

 inner corner of the internal nares, is a pair of tusks on a raised surface, 

 similar to those on the maxillaries and palatines. Running across the two 

 bones, from one of these areas to the other, is a low ridge, formed by a thick- 

 ening of the bone and covered with numerous fine teeth. Similar patches 

 of fine teeth lie in front of the tusks and run from the posterior edges of the 

 tusks around the opening of the nares and back to join the teeth on the 

 pterygoid. Each prevomcr divides posteriorly and receives a long, slender 

 prolongation of the pterygoid. 



_ The pterygoids are tripartite. An inner process unites with the stout 

 basipterygoid processes of the parasphenoid. The anterior portion forms 

 the main part of the bone; it is a wide, flat plate uniting with the palatines, 

 maxillaries, and prevomers externally. The inner edge is concave and forms 

 the border of the great palatine vacuity. This edge is thickened, and bears 

 on its whole length a series of small teeth; the series is continuous, anteriorly, 

 with the teeth on the prevomers. The posterior portion is turned so that 

 it is a vertical plate convex toward the mid-line and uniting with the pro- 

 squamosal above and the quadrate behind. 



The parasphenoid unites by strong sutures with the basioccipital behind 

 and with the pterygoids laterally. This posterior portion is not large, but 

 it is thickened and there is a considerable longitudinal depression on the 

 median line. The anterior portion, forming the bridge between the two 

 palatine vacuities, is relatively slender and ends in a rather sharp point 

 anteriorly. 



The basioccipital is a small but well-defined bone uniting strongly with 

 the parasphenoid. The interpretation given by Broili (3) (plate 8) of this 

 region, was based on a crushed specimen; the pterygoids do not meet in the 

 middle line and there is a single basioccipital bone behind the parasphenoid 

 Instead of two exoccipitals. 



The quadrate is a small, triangular bone between the pterygoid and 

 quadratojugal, on either side, and the prosquamosal above. It appears only 

 on the lower surface and for a short distance on the inner side of the pos- 

 terior prolongation. The condyles are shallow and the whole articulation 

 with the lower jaw was weak. 



On the posterior surface of the skull the foramen magnum appears as a 

 relatively very small, oval opening. The condyles are short and stout, with 

 concave articular faces looking slightly inward. The exoccipitals are de- 

 scribed by Branson as forming the edges of the foramen magnum, except 

 above, where it is completed by the supraoccipital plates. From the outer 

 side of the exoccipitals, a slender process runs out to the tabulare angle of 

 the skull, and between it and the supraoccipital plates above is a good- 

 sized foramen. In the otic notch, below, a stapes of good size has been 

 found in specimen No. 3060 University of Michigan. 



