I2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 134 
vascular canal before entering the foramen magnum. Medial to the 
hypoglossal foramen and extending ahead to the lateral margin of 
the basioccipital, a broad and distinct anterolaterally directed groove, 
evidently occupied by the internal carotid, as suggested by both Wort- 
man and Matthew, rises into the large aperture representing the fora- 
men lacerum medius just ahead of the medial portion of the petrosal. 
The exposed surface of the basisphenoid is triangular in shape with 
the anterolateral sides bound in part by the alisphenoids and forward 
by the V-shaped margin of the pterygoids. About midway forward 
on the anterolateral margin on each side, at the anterior extremity of 
a shallow groove from the foramen lacerum medius, there is a fora- 
men which extends forward above the pterygoid, eidently the ptery- 
goid canal for the Vidian nerve. Parallel and lateral to this on the 
surface of the alisphenoid are two or three sharp grooves or striae, 
extending between the posterior margin or lip of the foramen ovale 
to the position on the margin of the aperture corresponding to the 
eustachian foramen. Still more lateral and nearly parallel to the fore- 
going, but on the squamosal, is the straight and deeply impressed 
fissura Glaseri, for the chorda tympani nerve, sharply limiting the 
glenoid surface and postglenoid process medially and extending back- 
ward to a recess in the squamosal directly opposite the fenestra ovalis. 
The posterior surface of the postglenoid process shows a number of 
dorsoventral ridges and grooves near the lower margin, and a very 
broad and shallow depression near its medial margin extends upward 
and is confluent with a comparatively large postglenoid foramen 
(Wortman thought this to be absent) close to the fissura Glaseri. 
Petrosal.—The petrous portion of the periotic is exhibited in the 
anterolateral portion of the large otic fossa lateral to basioccipital. It 
does not appear to separate completely the foramen lacerum medius 
from the foramen lacerum posterius as the medial margin of the 
petrosal shown on the left side approaches close but does not touch 
the basioccipital. The outline of the petrosal as exposed ventrally can- 
not be fully determined because the margin is somewhat damaged 
and incomplete ; nevertheless the most conspicuous feature of this ele- 
ment is the downward- and forward-directed buttonlike promontorium. 
A fairly large fenestra rotunda faces backward and slightly outward. 
An elongate groove on the petrosal extending backward from a posi- 
tion immediately outward from the lateral margin of the fenestra 
rotunda is not explained but suggestion is made that this may have 
covered the stapedial muscle dorsally, or possibly the stapedial artery. 
The slightly smaller fenestra ovalis is forward and a little above the 
fenestra rotunda and faces laterally and somewhat forward. 
