THE SKULL. 35 



to a similar series of canals, not so well defined, on the external surface of that element. It 

 is evident, from the manner in which these canals converge and enter the supratemporal 

 fossa?, that the latter gave exit to the nerves and blood vessels that were distributed over 

 the surface of these bones. For greater protection, the larger of these .were incased in the 

 series of ramifying canals already described. 



THE POSTFRONTAL FORAMEN. 



The postfrontal foramen, a called by Professor Marsh sometimes the pineal foramen and 

 sometimes the parietal foramen, is usually situated between the postfrontals a little in advance 

 of the anterior extremity of the parietal and on a line with the posterior borders of the supra- 

 orbital horn cores. Since it does not function as a pineal foramen and is usually entirely 

 without the limits of the parietal and within the postfrontals, I have thought best to reject 

 both of the names hitherto applied to it and to call it the postfrontal foramen, from its 

 position in relation to the frontal region of the skull. It is well shown in the type of Tricera- 

 tops serratus (No. 1823, Yale Museum) and in most well-preserved skulls, though in old age, 

 in the genus Triceratops at least, it becomes partially or completely closed, as is the case in 

 the type of Triceratops prorsus (No. 1822, Yale Museum). A short distance below its exit it 

 branches and connects with that series of large cavities already mentioned as occurring at 

 the base of the frontal horn cores. It is possible that its chief purpose may have been to 

 convey nutrient blood vessels to the growing horn cores and their enveloping horny sheaths, 

 but if so this would fail to explain why they became closed in old individuals, since their 

 function would continue after the horn cores were fully developed, as the horny sheath doubtless 

 continued to grow throughout life. In the type of Torosaurus lotus (No. 1830, Yale Museum) 

 instead of a single median foramen branching beneath the surface there are two, one in each 

 postfrontal, separated by a distance of 21 millimeters and each apparently running directly 

 to the large cavity at the base of the horn core of its side of the skull. This character is not 

 persistent in this genus, since in the type of T. gladius (No. 1831, Yale Museum) there is a single 

 median foramen situated not in the postfrontal as in Triceratops, but in the anterior extremity 

 of the parietals. This foramen in this species might very properly be called the parietal foramen, 

 as was done by Marsh. 



THE LATERAL TEMPORAL FOSS^. 



These are two in number, situated one on either side of the skull, with the external openings 

 lying beneath and a little posterior to the orbits. The external openings are subtriangular 

 to ovate in outline and are inclosed anteriorly and superiorly by the jugals, posteriorly by 

 the squamosals, and inferiorly by the quadrates and quadratojugals. 



THE ORBITS. 



The orbits are large and deep, indicating that the organs of sight were highly developed. 

 The external border^of the orbit is very strong and anteriorly it extends outward, well beyond 

 the general external surface of the skull, so as to afford great protection to the eye. Apparently 

 there were no sclerotic plates or other ossicles especially developed for the protection of the 

 eye. The external opening of the orbit is broadly elliptical to nearly circular in some species, 

 with the larger diameter inclined backward at an angle of about 30° from the perpendicular 

 when the skull is in a horizontal position. The external border of the orbits is formed supero- 

 posteriorly and posteriorly by the postfrontals, inferiorly by the jugals, and supero-anteriorly 

 and anteriorly by the prefrontals and lachrymals, respectively. In the type of Triceratops 

 serratus (No. 1823, Yale Museum) the orbital fossae descend to a depth of 23 centimeters into 

 the body of the skull. They are directed downward and slightly forward and are separated 

 by a bony septum which seems to be pierced by a large foramen. Anteriorly the orbital cavities 

 communicate with the narial orifices by large vacuities. The optic foramen enters the orbital 



a Postfrontal fontanelle. — R. S. L. See footnote, p. 24. 



