72 PKOFESSOR STRUTHERS. 



ridge rises abruptly, like a finger laid along the middle of 

 the body, the foramina in some (7th and 10th) communicating 

 freely below it. This longitudinal bridge on the 8th, now 

 broken, has been constricted, or even wanting at the middle. 

 On the first five caudal it stands up as a triangular ridge, with 

 the depression and foramen, or foramina, at each side, narrow- 

 ing backwards to the 5th, where it is a sharp well-marked ridge. 

 On the 4th caudal it has again been undermined, so as to form 

 a bridge, so narrow that it has given way. On the 6th caudal, 

 and on the four succeeding vertebrae, those with neural arch 

 complete, it has entirely disappeared, the floor of the canal 

 being smoothly concave from side to side. After an interval of 

 four vertebrae (llth to 14th), which have a large median fora- 

 men, the median ridge reappears, on the 15th and succeeding 

 vertebrae, with a foramen or two on each side of it. 



This ridge must belong, as I found in the neck of B. musculus, 

 to the superior common ligament of the bodies. The 6th 

 caudal, on which it ceases as a ridge within the canal, is the 

 last vertebra with a pronounced transverse process. 



[This pronounced superior median ridge is a character of Megaptera, 

 as compared with B. musculus and B. borealis. In B. musculus, it is 

 seen in the neck, and very faintly on the two or three anterior dorsal, 

 not at all on the other dorsal, and very faintly on the lumbar and 

 anterior caudal ; in the posterior part of the lumbar region as a 

 broad low convexity, but not at all projecting as in Megaptera. In 

 B. borealis this ridge is even more completely absent, faintly per- 

 ceptible to the finger in the posterior lumbar region only.] 



Inferior Median Ridge. This sub-vertebral median ridge, 

 seen especially in the lumbar region of Cetacea, is strongly 

 marked both in depth and breadth about the middle of the 

 lumbar region in Megaptera. Beginning on the 1st lumbar it 

 is there broad and long ; on the 2nd it is sharp, but still has 

 the deeply concave outline. From the 3rd to the 8th this 

 crest projects so much as to give the body, on side view, a 

 convex outline below, strongly marked on the 5th and 6th. On 

 the 9th and 10th it is well marked, but the outline is again a 

 little concave. Viewed from below, the crest is seen on the 

 4th lumbar to broaden out posteriorly ; on the 5th, its posterior 

 f form a wide triangular surface, 2 inches broad behind ; on 

 the 6th, the whole ridge is broad, f inch at the middle, 



