ANATOMY OF MEGAPTERA LONGIMANA. 71 



and is about equal on both ends. The 9th and still more the 

 10th, have the posterior end more convex than the anterior ; the 

 llth, the first post-chevron vertebra, very much so. The 12th 

 and 13th, more especially the 13th, become decidedly bi-convex, 

 the posterior surface still the most convex, their curvatures 

 much resembling those of the human crystalline lens. The con- 

 cavity is not due merely to bevelling but is seen over the central 

 pulp-area also. Behind these two the plano-convex form is 

 resumed, the anterior end nearly flat, the convexity of the 

 posterior end less than that of the biconvex vertebrae. The two 

 biconvex bodies are those which follow, with one transition 

 vertebra between, after a complete neural arch and chevron 

 bones have ceased. This form of the bodies must give great 

 freedom of motion to this part. 



The caudal vertebrae, from and after the 14th, instead of hav- 

 ing the sides convex both ways, like the three just in front, are 

 pinched at the middle, rendering the sides concave vertically at 

 the middle. This gives a four-cornered shape, in antero-pos- 

 terior view, to these vertebras, in striking contrast to the cir- 

 cular form of the vertebrae in front of them. 



[In B. musculus the vertebrae continue flat-ended back to the 

 15th caudal (the first after the disappearance of a complete neural 

 arch), the posterior end of which is somewhat convex. This in- 

 creases on the 16th, and the plano-convex form is continued on the 

 vertebrae behind, but there are no bi-convex vertebrae in this B. 

 musculus. The four-cornered form begins on the 18th caudal, but 

 is not very well marked till the 20th. The pinching at the sides is 

 rather in the form of an obliquely upward and backward fossa than 

 that of the vertical concavity of the middle of the side presented by 

 Megaptera. In. B. borealis the 12th and 13th caudal, and to a less 

 extent the 14th, are bi-convex.] 



Superior and Inferior Median Ridges of the Bodies. 

 The sharp superior 'median ridge seen on the bodies of the 

 cervical vertebrae flattens down on the anterior dorsal into a 

 low broad median convexity. Increasing as we go back, this 

 elevation at the 5th dorsal has assumed a definite form 2 

 inches in breadth with a definite oval foramen, it may be 

 more than one foramen, on each side of it. At the 

 beginning of the lumbar region it is more raised and nar- 

 rowed to 1 \ inch, and bounded by a more elongated entrance 

 to the foramen. From the 7th to the 10th lumbar the 



