HOLLAND : THE OSTEOLOGY OF DIPLODOCUS MARSH 231 
slightly subtrilobate in outline.” The condyle is missing in Marsh’s specimen No. 
1922 (U.S. N. M., No. 2675) and he evidently based his description on specimen 
No. 1921 (U.S. N. M., No. 2672). The lower side of the bone in advance of the 
condyle is deeply concave longitudinally and convex transversely, throwing forward 
and downward a broad hypapophysis, which is divided into two portions, or basi- 
occipital processes, at its anterior extremity. These processes point downward and 
backward. (See Figs. 3-5.) The body of the bone articulates by rough sutural 
surfaces with the basisphenoid, and the exoccipitals. 
The Exoccipitals (Figs. 4-6, and 10).—The exoccipitals are broadly and 
strongly developed. heir inner margins, which are concave below, form the sides 
and the top of the foramen magnum in such a way as to show no trace of a suture 
in all specimens which the writer has examined. They send outward strong par- 
occipital processes, which are expanded above near their origin and again at their 
extremities. A sinus is thus developed upon the upper margin of the processes, and 
this forms the lower margin of the postternporal fossa located between the paroc- 
cipitals and the squamosals, which by Professor Marsh was styled the ‘“ posterior 
”) 
The paroccipital processes articulate on the anterior surface of their outer 
Fia. 4. Posterior view of back of skull of Diplodocus (No. °°? Car. Mus. Cat. Vert. Fossils, one half natural size). 
0.C., occipital condyle ; LX., exoccipitals ; S.O., supraoccipital ; PA., parietals; SQ.,squamosals ; P.F., postfrontals ; 
P.O., postorbitals ; AS., alisphenoids ; P.OC., paroccipital processes of exoccipitals ; b.0.p., basioccipital processes ; b.pt., 
basipterygoid processes; 1, foramen magnum ; 2, posttemporal fosse ; 3, supratemporal fosse ; LY., glossopharyngeal 
foramina ; XJJ., condyloid foramina. 
