ANATOMY OF MEGAPTERA LONGIMANA. 153 



form in B. musculus contrasting with the semilunar form in 

 Megaptera. 



The anterior boundary of the temporal passage is formed 

 by the thick posterior border of the supra-orbital plate of the 

 frontal bone, rounded by the bone turning downwards and for- 

 wards like a scroll, bounding the orbital cone posteriorly, and 

 forming a pulley-surface for the play of the temporal muscle. 

 In Megaptera it is directed a little backwards, with slight con- 

 cavity ; in B. musculus it slopes forwards in its whole length. 

 (Thickness at the inner, middle, and outer parts, in Megaptera 

 6, 3J, and 2 inches; in B. musculus, 5, 3, and 1J.) The direc- 

 tion of this great post-orbital bar is determined by, or deter- 

 mines, the direction of the orbit. 1 



5. DIFFERENCES OF THE BONES FORMING THE TEMPORAL 

 FOSSA AND PASSAGE. The bones to be noticed here are the 

 parietal, at the fossa and passage, and behind and below the 

 orbital cone ; at the inner part of the passage, the temporal, 

 sphenoid, and pterygoid ; below the passage, the pterygoid, 

 temporal, and palate ; and, behind and below the orbital cone, 

 the pterygoid as well as the parietal. 



The parietal bone has much greater expansion on the fossa 

 in Megaptera than in B. musculus, covers the inner wall as far 

 forwards as to about 3 to 4 inches from the anterior edge of the 

 fossa, and extends outwards on the floor to a breadth of from 

 6 inches at the middle of the fossa to 8 inches at the bar, and 

 out upon the back of the bar for 13 inches as a thin lamina. 

 In B. musculus it covers only the inner wall, forwards to within 

 about 6 inches of the anterior edge of the fossa, none of the 

 floor, and does not reach out on the bar. Where the bar is 

 covered by the parietal in Megaptera, it is rough in B. musculus, 

 along fully its inner half, and was in the recent state covered 

 by cartilage. The parietal is seen to cease by a natural edge 

 1 inch internal to this rough part. On the posterior wall of the 

 temporal fossa and passage, the parietal goes outwards farther 



1 In this connection it is interesting to note the different direction of this 

 great bar in the different Finners. Its direction in Megaptera and in B. musculus 

 is noted above. In B. borealis it is directed considerably backwards, giving the 

 supra-orbital plate great breadth externally and its square form. In B. rostrata 

 still more backwards, giving a rhomboid plate. 



