142 PROFESSOR STRUTHERS. 



inches external to what would be its end in B. musculus, giving 

 the notch its outward obliquity. Prolongation of this border 

 would have carried it upon or behind the point of the posterior 

 process of the sternum. It therefore stops short when it arrives 

 below the wing. Thus the narrowness of the anterior aperture 

 of the thorax and the sloping direction of the rib account for 

 these modifications of the end of the first pair of ribs, as well as 

 for the form of the wing and posterior parts of the sternum, 

 and for the difference in the mode of articulation, as compared 

 with B. musculus. 



[The very different proportions of the sternum in the B. mnsnd'us, 

 compared with Megaptera, are seen in the meastiremcnts in the 

 table (Table VII.). The wings are very long transversely, and more 

 expanded near the end than at their middle ; the posterior process is 

 long and bent downwards, more than the cervical process is. The 

 cervical process is much narrower than in Megaptera. The whole 

 bone is thinnei\ The parts of the edges the ossification of which is 

 luifinished, are, the outer edge of the wing, ;j to | inch thick (the 

 })osterior slope of the end thicker than the anterior, the surface 

 facing obliquely upwards) ; part of the point of the posterior process ; 

 and parts of the anterior convex border of the cervical process, 

 thinnest (^ inch) at the middle (the most pi'ojecting part), a little 

 thicker (^ inch) on each side. Along the posterior § of the cervical 

 process the border is quite sharp and finished. It is not evident how 

 this sternum could bifurcate forwards, or how their thin edges could 

 grow so as to fill up the great hollow between the wing and the 

 cervical process.] 



The Chevron Bones. 



40. Characters in Comparison w^ith those of B. 

 Musculus. — The chevron bones in this Megaptera are 10 

 in number, the first and the two last in separate halves. 

 The number in the B. musculus is 13, in the B. borealis 15. 

 It is easy to distinguish those of Megaptera from those of the 

 other two finners. As seen in the table of measurements given 

 below (Table VIII.), the arch in all of them in Megaptera is 

 much wider at the middle than at the top, the space having the 

 form of the lower § of an ellipse or of a rather pointed oval. 



[In B. 7miscnlus the space in the first three is a wide triangle, 4 

 inches deep, 3| across, the lamina) not coming at all towards each 

 other at the top. On the 4th, they begin to approach a little at the 

 top, rendering the space a little narrower there than a short way 

 below, and this increases backwards, but not so much as in IMcgaptcra 



