ANATOMY OF MEGAPTERA LONGIMANA. 133 



tion, which is increased by the lower part being prolonged backwards 

 into a blunt point. Two parts may be recognised — the upper, sloping 

 upwards and outwards, is seen in the end view to ftice obliquely back- 

 Avards, to be nearly vertical, and to be separated from the chief part 

 by a gentle concavity, reaching upon it from the posterior concave 

 margin. The part thus marked off appears to be that which projects 

 above the fossa. The lower and chief part faces inwards, is more 

 decidedly convex antero-posteriorly than the upper part, and has the 

 oblique direction downwards and backwards. This lower part of the 

 articular surface, as seen in the end view, is pointed below on the first 

 three ribs ; from the 5th to the 8th broadest below ; on the next 

 three the terminal torsion is so miich diminished that the point of 

 the lower part is downwards rather than backwards; on the 12th, 

 13th, and Hth the end is rounded, but greatest vertically.] 



In Megaptera.— As compared with those of B. musciilus, the 

 most striking difference at the vertical end of the ribs in Megap- 

 tera, behind the 3rd, is the lowness and rounding off of the 

 angle. The concavity between the tubercle and angle, on the 

 external neck, is much less, is very slight after the 7th, and 

 after the 9th or 10th is not present. The gentle elevation 

 corresponding to the angle in B. musculus diminishes and dis- 

 appears at the same stages of the series. The slightness of the 

 constriction is owing also to the filling up of the external neck, 

 the upper border of which, on the anterior seven, slopes a little 

 upwards to the low angle. This gives the upper 12 inches or 

 so of the rib a greater bend down than in B. musculus, and a 

 broader external neck compared with the breadth of the shaft. 

 This direction of the upper part of the rib and the lowness of 

 the angle may be considered as related to the upward direction 

 of the transverse processes, in below the ends of which they are 

 received, although that direction of the transverse processes is 

 continued farther back on the series. 



The first rib has a rounded top, from the low angle inwards, 

 tapering downwards and inwards to a blunt point. The inner 

 half (3 inches) of this may be assigned to the beak (best marked 

 on the left rib — see fig. 18), much turned back on its last H 

 inch ; but there is no distinct tubercle, and only the blunt point, 

 about 1 inch thick, has been covered by cartilage. The second 

 rib has a prominent tubercle, the end sloping obliquely 

 downwards and inwards, giving a broad triangular beak, If 



