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 5 x 3 -g-th 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- 



