ANATOMY OF MEGAPTERA LONGIMANA. 135 



part is curved backwards, is much rounded off as it ascends, and 

 faces obliquely backwards, while the lower part (f) faces inwards, 

 and is more convex in both directions. When the rib is applied 

 naturally to the vertebrae, the concavity on the articular end 

 corresponds to the fore part of the upper boundary of the fossa ; 

 the upper part rises above the fossa, curving towards the back 

 part of the upper edge of the fossa, but, as the outer edge of 

 the transverse process is thick (1 inch at the middle, more in 

 front, less behind) the rib does not seem as if it had risen above 

 the level of the cartilage with which the process has been 

 tipped ; and the lower f of the rib, more ball-like, occupies the 

 anterior part of the fossa, the axis corresponding to that of the 

 fossa, the direction downwards and backwards. The measure- 

 ments of the end of the 7th rib are height, almost 4 inches ; 

 breadth, below middle, If. Those of the fossa on the 7th 

 transverse process are antero-posteriorly, at middle, 2| inches ; 

 externally, 3 ; vertically, 3 ; depth, \ inch. The end of the 10th 

 rib is If inch broad below the middle ; the 10th fossa, antero- 

 posteriorly, 3 \ inches ; vertically, 4 ; depth, f inch. But the 

 edges of the fossae are not completely ossified. The fossa faces 

 downwards, and also outwards and backwards, the end of the 

 rib upwards and inwards. The more sloping form of the ends 

 of the ribs in Megaptera (from the less projection at the top) 

 than in B. musculus corresponds to the more inwardly elongated 

 direction of the fossae in Megaptera. The articular ends are all 

 broader in Megaptera than in B. musculus. No part of the 

 costal fossa3 in Megaptera appears to have been covered with 

 cartilage. 



The different form of the costo-transverse articulation in 

 Megaptera, compared with B. musculus, has the result that 

 there is more extensive contact of the opposing surfaces in 

 Megaptera. The fossae are more elongated vertically or trans- 

 versely, and, spoon-like, receive a broader head. This difference 

 may have reference to the much greater massiveness of the rib. 

 But dissection of the ligaments and of these parts in their 

 natural relation will be necessary for a complete explanation of 

 the differences. 



