160 PROFESSOR STRUTHERS. 



begins narrow and shallow (width | inch behind, narrowing distally, 

 depth I inch) compared with that of Megaptera. External to the 

 sharp and raised inner border is a shallow groove, |- inch broad, 

 tapering distally. The snperficial surface is broader and more deeply 

 grooved than in Megaptera ; from edge to edge at the peak, the 

 depth of the hollow is about 2 inches, in Megai^tera about half as 

 much. The greater depth of the concavity on the distal half in B. 

 musculus is owing to the outer margin not being so low (only 1 inch 

 lower than the inner margin at the peak), and to the surface bending 

 rapidly down to meet the inferior surface. The free border of separa- 

 tion is so far down, and the fiill is so rapid, that the distal half of 

 the superficial surfoce looks almost like a distal surface, like the 

 transversely hollow base of a four-sided pyramid. The two nasals 

 together of B. musculus are not unlike a cocked hat. The peak is as 

 if the distal 2 inches of it in Megaptera had been cut off vertically; 

 its two borders form just a little less than a right angle, and both 

 belong to the superficial surface. A nearly vertical symphysis is thus 

 formed below the peak, about 21 to 3 inches long, until the sharp 

 distal border is reached which separates the inferior from the super- 

 ficial surface. The inferior surface is, at the outer part, moderately 

 inclined towards its fellow ; on their inner part, rapidly so, making 

 a wedge-shaped recess of the inner part of the roof, 2 inches across, 

 n high-] 



These differences between the nasal bones of Megaptera and 

 B. musculus are greater than it is easy to bring out by general 

 measurements or drawings. 



11. Posterior Nares. — The form is semilunar, broader at 

 one end, convexity above, the long axis inwards and forwards 

 and a little upwards. The broader end is in Megaptera the 

 inner, in B. musculus the outer. The obliquity is much less in 

 Megaptera, inner end 2 to 3 inches anterior to outer end ; in 

 B. musculus 6 inches. They are smaller in Megaptera, long 

 diamater 6 inches ; vertically, at outer third 3 inches, at middle 

 3|, at inner thii'd 3f. In B. musculus the same measurements 

 are respectively 8|, 4|, 4|, 4. The width of the posterior nares 

 together, transversly, opposite their anterior ends, is in Megaptera 

 12| inches, in B. musculus 14|^ inches. 



Farts near the Posterior Nares. — Here there are marked 

 differences. Tn Megaptera the slanting edge of the vomer is 

 shorter (length 8 to 9 inches), and begins close to the posterior 

 end of the bone, as a low ridge, and at the nares it is a 3-inch 

 high septum, and very thin (5 to | inch at mid-height there). 

 In B. musculus, instead of a ridge there is a shallow median 



