172 PROFESSOR STRUTHERS. 



show that the height is the same in both, that in Megaptera 

 the breadth is greater by J part (2 inches), the length less by 

 J part (4 inches) than in B. musculus. This accords with the 

 proportions of the back part of the skull externally, but the 

 whole cavity appears to be more capacious in B. musculus. The 

 opening of the olfactory fossa is triangular in form, base below, 

 and smaller in Megaptera ; in B. musculus bluntly triangular, 

 base above with a narrow notch at the middle (Megaptera, 

 breadth 3 inches, height 2 ; B. musculus, breadth 3J, height 3). 

 The fossa itself in Megaptera is directed more upwards, is 

 curved, and is shorter than in B. musculus (Megaptera 4 inches, 

 B. musculus 5). 



Other Characters within the Cranium. In Megaptera the 

 suture between the post and pre-sphenoid (10 inches from the 

 foramen magnum) is open across its whole breadth ; in B. 

 musculus there is a short transverse ridge at the middle in the 

 corresponding position (12 inches from foramen magnum), but 

 no suture visible. Where the basi-occipital and post-sphenoid 

 appear to have united, there is in Megaptera (5 inches from the 

 foramen magnum) a curved ridge, as prominent nearly as a 

 finger laid on flat, curved, convexity backwards ; in front of it a 

 wide shallow fossa ; going back from it a similarly raised median 

 ridge, on each side of which is a rounded fossa. In B. musculus 

 the transverse ridge (8 inches from the foramen magnum) is 

 very low, the median ridge behind is well marked but broad, 

 and there is no fossa at the side of it. The sella turcica, about 

 3 inches long in both, is better marked in Megaptera, having a 

 transverse depression on its anterior half; in B. musculus there 

 is rather a transverse convexity, with a slight longitudinal 

 median depression. The common orbital foramen, representing 

 the optic foramen and sphenoidal fissure (which are separate in 

 B. rostrata), is in Megaptera partly divided into optic and 

 sphenoidal fissure parts by a well-marked peak of bone above 

 and below, the interspheneid suture intersecting the lower peak. 

 If this partial subdivision did not exist in Megaptera, the com- 

 mon foramen would form a triangle wider below than the common 

 foramen in B. musculus. In the roof of the cranial cavity there 

 is a well-marked sharp median ridge in B. musculus, much less 

 developed in Megaptera. 



