126 



PROFESSOR STRUTHERS. 



Taken along the outer border the lengths of the 6th ribs are, 

 Megaptera 80 inches, B. musculus 82. 



Breadth. — The greater breadth of the first rib in Megaptera 

 is on the right side only and not throughout, as the following 

 measurements show, in inches: — 



On its lowest 6 inches the first rib is deeply excavated an- 

 teriorly on more than half of its breadth (see fig. 18). This 

 peculiarity belongs to its relation to the sternum. In B. 

 musculus this notch is not present, the rib passing of full and 

 increasing breadth in below the wing of the sternum. A shallow 

 excavation, | to f inch deep, is seen on the lower part of the 

 anterior border of the 2nd rib in Megaptera. 



On the 2nd, 3rd, and 4th the breadth is greatest in B. mus- 

 culus. From the 7th back to the 12th, greatest in Megaptera. 

 On the 14th Megaptera loses, being the last rib. To the 

 eye it appears evident that in Megaptera the more anterior 

 ribs are narrower, and the posterior ribs broader, than in 

 B. musculus. 



In Megaptera the external neck is broader than in B. musculus, 

 except on the 1st and 2nd, and is the broadest part of the bone 

 except on the 1st and last, on the 2ud and 3rd very much the 

 broadest part ; all the shafts are narrowest at their lower end 

 except the last ; the broadest part of the shafts is below the 

 middle, on the third quarter of the bone. In B. 'musculus the 

 broadest part of the shaft is at about the middle of the lower 

 half; on the lower quarter of the bone the breadth diminishes 

 downwards, except on the 5th and 6th ribs, which rather increase 

 in breadth to the end ; from the 4th to the 13th the breadth is 

 greater at the middle of the upper half than at the middle of the 

 bone. The ribs of Megaptera and B. musculus, therefore, differ in 

 breadth at different parts thus : — In B. musculus, external neck 



