ANATOMY OF MEGAPTERA LONGIMANA. 141 



occupying 3 to 4 inches. This corresponds to the hinder slope of the 

 outer end of tlie wing of the sternum, j 



In Megaptera there is no separated mark on the rib indicating 

 a distinct lateral costo-stemal articulation, simply the border 

 of the rib is thick and rough for its last 7 to 8 inches, in marked 

 contrast to the character of the border of the rest of the rib. 

 This rough part extends 2 to 3 inches farther up the rib than 

 the level of the fore part of the end of the wing of the sternum, 

 as placed in fig. 18. 



This border of the rib, on the right side, terminates in a pro- 

 minent angle or process, the end of which shows a sub-carti- 

 laginous surface, Ih inch by 1 inch. The mode of articulation 

 I infer to have been by continuous ligamentous attachment, 

 externally, to the last 7 or 8 inches of the rib and to the cartilage 

 on the terminal process of this border of the rib ; internally, to 

 the cartilage of the wing of the sternum and to the rough mark 

 on the hinder border of the wing and side of the base of the 

 posterior process. On the left rib there is no terminal process 

 to the anterior border of the rib, simply a rounded-off. angle, 

 without thickening, but it appears to have been covered by 

 cartilage. As shown in fig. 18, the left first rib is shorter at 

 the lower end than the right by I5 inch. 



Whether the wide oblique notch in the end of the first rib is 

 exceptional in this Megaptera I have not the means of deter- 

 mining. The edge is thin, and as if finished on the right rib, 

 but on the left a thin strip of cartilage appears to have been 

 continued on the anterior part of the notch. The notch, or 

 excavation, is on the right rib 4 inches in length, f inch in 

 depth ; on the left rib 5 inches in length, f in depth. The pro- 

 jecting end of the rib behind the notch is 3 inches in breadth, 

 1 inch in thickness towards the posterior end, and has been 

 covered with cartilage. The end of the rib, therefore, has, as in 

 the adult B. nmsculus, two cartilages — the anterior, by which it 

 articulates with the sternum ; the posterior, a long way behind 

 the sternum. Between these, in the adult B. musculus, is a 

 thin finished edge of bone. In Megaptera this thin part is still 

 less developed, so that there is a wide notch between the parts 

 bearing the posterior and the anterior cartilages. But, further, 

 in Megaptera the rib stops short on its anterior border several 



