478 ALLIS. [Vot. II. 
very thick, and is directed backward and outward. It sends a 
large branch backward to about the middle of the bone, and 
another forward toward the eye, in front of the main canal, 
both of them branching several times, and having in all thirty- 
seven openings, all lying in front of the middle point of the 
bone, and extending almost to its extreme anterior edge. 
The canal, after leaving the upper postorbital, enters the 
postfrontal, where it has a curved course, turning gradually 
backward till it reaches the median edge of the bone at about 
its middle point. Here it turns directly backward, and, running 
between the frontal and postfrontal, enters the squamosal at 
about the middle of its anterior end. It traverses this bone 
from end to end, running directly backward with a slight lateral 
bend near the hind end, where it is joined by the opercular 
canal. 
In the postfrontal, the canal lies entirely in what Sagemehl 
(No. 13, pp. 184 and 185) considers merely the outer, denser, 
and harder part of the primary ossification of the postorbital 
process. This ossification, which is traversed by a canal of the 
lateral system, and the prefrontal, which is not, are both con- 
sidered by him as exceptional instances of primary ossifica- 
tions that have acquired secondarily the surface characteristics 
of true dermal bones. He calls attention to the earlier work 
of Bridge (No. 4, p. 607), who describes each of these bones 
as having an outer dermal component wholly separate from the 
underlying primary ossification; but he nevertheless strongly 
asserts that this separation can only be made by fracture. 
In the several specimens which I have examined with special 
reference to this point, I have always found the prefrontal a 
single bone and the postfrontal in two parts. The prefrontal 
(Cut 2, gvf) lies under the outer anterior corner of the frontal, 
projecting slightly beyond it, but in no place rising above the 
level of its under surface. The projecting edge is continuous 
with the edge of the frontal, which in this place is bevelled, and, 
although roughened, it has neither the character nor appearance 
of the outer surface of the dermal bones. In the unprepared 
head it is covered by thick dermis, and its roughened edge gives 
attachment to strong membranes. It lies deep and is not 
traversed by the main cranial canals or any of their branches. 
The dermal portion of the postfrontal (Cut 2, psf) is a small 
