160 PROFESSOR STRUTHERS. 



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

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

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

 tapering distally. The superficial 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 Megaptera 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 fall is so rapid, that the distal half of 

 the superficial surface 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 2J 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, 

 1 J 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 

 3J, at inner third 3f . In B. musculus the same measurements 

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

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

 12 J inches, in B. musculus 14 J inches. 



Parts near the Posterior Nares. Here there are marked 

 differences. In 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 (J to f inch at mid-height there). 

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



