ANATOMY OF MEGAPTERA LONGIMANA. 139 



care, the rib lies behind the wing of the sternum. The adapta- 

 tions in the developed bones present several points of interest. 



[To understand these in Megaptera it is necessary to refer to the 

 adaptations in B. musculus. As seen in my figure of the parts, still 

 in their natural connection (loc. cit., 1871), there are two places of 

 articulation (1) the lateral costo-sternal joint. The end of the wing, 

 covered by cartilage, is joined on its posterior edge by ligaments to 

 the anterior border of the rib, where a rough mark is seen. (2) Ter- 

 minal costo-sternal joint. The end of the rib advances towards the 

 posterior process of the sternum, and the short cartilage belonging to 

 the anterior part of the end of the rib is joined to the sternum by 

 ligament. The rough mark for this articulation is very evident in 

 the 50-feet-long B. musculus, on the angle between the wing and 

 posterior process, and on the anterior half of the side of the process, 

 which is specially broadened at this part. The great length, trans- 

 versely, of the wing of the sternum in B. musculus gives room for a 

 considerable space between the lateral and terminal joints. Viewing 

 the end of the rib in the 50-feet-long B. musculus, it is seen to be 

 divided into three parts an anterior, 1 \ inch thick ; a narrow middle 

 part, \ to \ inch thick ; and a posterior part, f to 1 inch thick. In 

 the 64-feet-long B. musculus the narrow middle part is a sharp- 

 finished edge, the anterior and posterior parts broad, and each covered 

 by cartilage. The anterior cartilage is at the terminal costo-sternal 

 joint, the posterior cartilage is free and non-articular, and is a long 

 way behind the sternum. The narrow middle part is the most pro- 

 jecting part of the rib, the free border receding from it, covered by 

 the posterior cartilage. 



In my B. borealis the soft parts here have been preserved, and 

 throw light on the transition from B. musculus to Megaptera. Ex- 

 ternally is seen the lateral costo-sternal articulation, as in B. muscu- 

 lus, the cartilage belonging to the sternum. Internally, after a short 

 interval, owing to the shorter wing, the cartilage, which has been 

 detached from the rib, is, like the end of the rib itself, 6 inches in 

 breadth, and almost separated by a narrow middle part into an 

 anterior and posterior part. The anterior and smaller part, 1 ^ inch 

 in length, close to the sternum, is joined to it by ligament, to the 

 angle formed by the wing and a special projection from the side of 

 the base of the short posterior process ; the posterior part, 2^ inches 

 in length, is joined to the fibrous membrane which fills up the great 

 gap (5 inches deep) behind the sternum, and between the greater part 

 of the free ends of the first pair of ribs. The end of the rib recedes 

 behind the narrow middle part, but the cartilage that covers it projects 

 internally, to the extent of 1^ inch posteriorly, and thus gives the 

 whole cartilage of the end of the rib a deeply notched or scooped-out 

 form, obliquely, resembling the scooped-out end of the long rib in 

 Megaptera.] 



There is no evidence of the presence of two joints in Megap- 

 tera, but rather of one continuous oblique ligament ous con nee- 



