ANATOMY OF MEGAPTERA LONGIMANA. 105 



nected with the better development of the posterior articuhir pro- 

 cesses ill B. musculiis. By this expansion the sjiinous process in B. 

 niusculus gains a breadth on an average of about 1 inch, or more. 

 It is well seen from the middle of the dorsal region back to the 1st 

 caudal, rather increasing as we go back to near the end of the lumbar 

 region. This prominence renders the posterior border of the spines 

 very concave. In Megaptera it is pronounced only on the last 

 lumbar and 1st caudal ; back at least to the last few lumbar it is so 

 low as to be only enough to give a convex outline to the spine and 

 lamina, viewed together. 



Length, Breadth, and Thickness of the Spines. — In length they increase 

 from the 1st dorsal (3| inches) to the 10th lumbar (18|, the 9th and 

 11 til each 18 inches), and then decrease backwards to the 1st caudal 

 (13|), finally ceasing on the 14th caudal. In breadth, at the top, 

 they increase backwards to the 14th dorsal (8|^ inches, breadth at 

 middle, 5i), and decrease from the 15th, but there is not much 

 diminution till after the lumbar region (1st caudal, 7J;, breadth at 

 middle, 5). In breadth at the middle, the difference from the 7th 

 dorsal {b\ inches, breadth at top, 6|) to the 1st caudal is not great ; 

 the broadest, the 9th, 10th, and 11th, are 6 inches, with breadth at 

 the top of 7|^ inches. In thickness, they are considerably less than 

 in Megaptera, although in B. musculus the processes are longer and 

 broadei'. At the middle they increase in thickness from ^ inch on 

 the 1st dorsal to | on the 6th dorsal, to f on the 10th dorsal ; con- 

 tinue pretty steady at f or | back to the 2nd caudal, after which 

 they decrease to | inch to the 7th caudal. 



The narrow ovoid upper border is seen from the 8th dorsal to the 

 13th lumbar (10th dorsal, at middle |, on posterior third f ; 14th 

 dorsal, | and 1 ; 1st lumbar, f and 1^; 11th lumbar, | and 11 ; no 

 other exceeds \\). On the 14th lumbar the end is contracted at 

 the middle, and on the last lumbar and first four caudal the ovoid is 

 reversed, the broader end forwards, ^ inch broader than at the 

 middle. Comparing the thickness of the ends with that of the 

 middle of the shafts, the thickness is the same in front of the 9tli 

 dorsal and behind the 5th caudal. From the 8th dorsal to the 13th 

 lumbar, the thick part of the ovoid is thicker all along than the 

 shaft ; but the middle of the ovoid is thinner than the shaft by fi'om 

 1 to f inch. The ends are more finished here than in Megaptera. 

 With thinner processes, the increased thickness on the posterior third 

 of the end is relatively greater than in Megaptera. 



Direction. — The spinous processes differ from those of Megaptera 

 in direction. Those of the 1st and 2nd dorsal are directed forwards. 

 The backward slope begins in both on the 7th, is less in the dorsal 



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