PEOFESSOE OWEN ON THE SCELIDOTHEEE. 
103 
The loose tympanic bone is wanting. The eustachian groove (e) is plainly traceable from 
the fore-part of the auditory ca\dty, expanding to behind the base of the pterygoid plate. 
The superoccipital extends upon the upper surface of the cranium in an angular form 
for more than an inch between the parietals. The temporal ridges are separated from 
each other by an interspace of only 8 lines, at the narrowest part of the intervening 
space upon the parietals, in the mid-line of which space is a longitudinal furrow. 
The sutures between the parietal, the occipital and the temporal bones, remaining in 
one of the crania of the Scehdothere in the British Museum, show the same small vertical 
extent of the long squamosal as in the young individual first described*; and the suture 
dividing the mastoid and squamosal below from the parietal above forms an irregularly 
undulating, almost straight line to opposite the end of the zygomatic process, where it 
descends and defines the subangular anterior boundary of the squamosal. At this point 
the squamosal appears to touch the frontal, an angular process of which extends back- 
wards to the foramen ovale (Plate VIII. fig. 2 1 ), dividing the fore-part of the squamosal 
from the pterygoid ; the three bones appear to concur in forming that foramen. 
The zygomatic process, commencing by the ridge continued from the temporal one, as it 
passes from the parietal to the temporal bone, has an antero-posterior extent of attachment 
of 3 inches 8 lines ; the free projecting end docs not exceed I^ inch in length : it is obtuse, 
with a slight notch below. The interspace between it and the squamosal plate is I^ inch. 
The process (Plate VIII. figs. I & 2,27) is trihedral, the outer side almost flat, a little concave 
behind and as much convex in front : the upper surface forms vrith the narrow squamosal 
plate a deep and wide channel, which lodged the lower border of the temporal muscle : 
the under side is the shortest and broadest, and forms the almost flat subtriangular 
surface (Plate IX. ff) for the articulation of the mandible. This surface differs from the 
more concave one of the Megathere, in the absence of any defensive ridge or promi- 
nence for the joint either behind or . externally. 
The pterygoid plates (Plate IX. 24) articulate with the sides of the basi- ( 5 ) and pre- ( 9 ) 
sphenoid, leaving a free interspace along the under surface of those bones an inch vride at 
its back part and gradually narrowing to the rounder styliform prolongation of the pre- 
sphenoid ( 9 ). The posterior border of the pterygoid slopes very obliquely from above down- 
wards and foiwards, and then more gradually rises with an irregularly undulating outline 
to blend with the palatine ridge (20), continued to the back part of the alveolus of the last 
molar. The combined palatines and pterygoids form a long and wide concavity, in 
which the oblique ridges, diverging fr-om the back part of the bony palate, deflne the 
acutely angular contour of the posterior palatal margin, and at the same time the lower 
boundary of the posterior nasal aperture (ib. n) ; this apertine, by the production of a 
ridge from the pointed end of the presphenoid, is shaped like a heart on playing-cards ; 
it gradually expands into the capacious pterygo-palatine fossa (ib. n, w, 24, 24). 
The parietals (Plate VIII. flg. 2 , 7) are quadrate bones, 6 inches in fore and aft extent: 
the posterior boundary of the frontals (ib. n) is 8 inches from the occipital ridge ; the 
* Zoology of H.M.S. Beagle, “Eossil Mammalia,” p. 73. 
p 2 
