264 Proceedings of the Royal Physical Society. 
less than it really is. The frontal and premaxillary bones, 
as already described, are much larger in the American than 
in the African skull ; and as the parts of these bones which 
form the boundary of the anterior nasal aperture are also 
broader, thicker, and more expanded from side to side, there 
is a corresponding difference in form and size of the anterior 
nasal aperture in the two skulls. The posterior nasal aper- 
ture is somewhat less in the American skull. 
The left bulla tympani is present, but without any open- 
ing ; it is of an oval shape, keeled beneath, an inch and a 
half in length, an inch broad, and rather more than half an 
inch in thickness. It is attached in front by a short twisted 
process to the anterior portion of the pars petrosa, and by 
another larger transverse process behind. There is a deep 
oval depression at the upper and back part, a third of which 
is open above and a little in front, the roof being formed by 
the under concave surface of the anterior process of the 
petrous bone, which is lodged in a deep cavity at the under 
and back part of the root of the zygomatic arch. The pars 
petrosa and the posterior process occupy another depression, 
formed partly by the root of the zygomatic process and 
partly by the mastoid bone. The posterior process of the 
pars petrosa slightly projects externally by a transverse 
opening more than an inch in length, and half an inch from 
above downwards, situated between the occipital and mas- 
toid bones, corresponding to the position of the foramen 
mastoideum. The anterior and posterior processes of the 
petrous bone, which are quite distinct in the Baleen cetacea, 
are so compressed together with the petrous part in this 
skull, as to appear to form but a single bone, about 2 inches 
in length, and rather less in breadth. 
The lower jaw is less massive than that of the African 
skull. Its length on each side, from the incisive edge to 
the angle of the jaw, is 7 J inches, and the depth about 
2 inches. The perpendicular height from the angle to the 
condyle is 5fVth inches, and the posterior part of the rami 
curves upwards from the angle towards the root of the 
condyle, but is nearly straight in the African skull. The 
distance from the condyle to the anterior point of the co- 
