ANATOMY OF MEGAPTERA LONGIMANA. Ill 



than in Megaptera, but in the 50-feet-long B. musculus it is the 

 reverse ; breadth at the narrowest part in Megaptera 3 inches, 

 in the B. musculus 3J ; at the widest part below in Megaptera 

 3, in the B. musculus 4J. Between these points is the place 

 of attachment of the transverse ligament. It may be that the 

 narrowing of this part of the canal depends on age. 



Parts on the Neural Arch of the Atlas. The true articular 

 processes which I described (1872, loc. cit, p. 39) in B. mus- 

 culus are present in this 50-feet-long B. musculus, oval facets 

 If inch transversely by 1J longitudinally; those of the atlas 

 received obliquely between those of the axis, the typical rela- 

 tion of true zygomal processes. In Megaptera there is no trace 

 of such articular contact, or of processes on the atlas, but 

 distinct and large processes project here from the axis in the 

 same position as the projections on which the articular facets 

 occur in B. musculus. They are about 1J inch in length, and 

 fully 3 inches broad at the base, narrower and rounded off at 

 the end. When the bones are placed in position, these anterior 

 articular processes of the axis overlap the lamina of the atlas for 

 fully 1 inch, but there is no actual contact, a space of about 

 J inch intervening between them and the arch of the atlas. 



Transverse Foramen of the Atlas. In all the specimens of 

 B. musculus the outer opening of this foramen or canal is oval 

 vertically, the lower and outer end prolonged as a groove. In 

 Megaptera the oval is nearly reversed, the ends anterior and 

 posterior. This is owing to the roof of the canal being con- 

 tinued farther outwards in Megaptera. From the same cause 

 the canal is longer by half an inch in Megaptera (If inch) 

 than in the 50-feet-long B. musculus. It is also rather smaller, 

 in Megaptera admitting the forefinger, in B. musculus admitting 

 the thumb. In all the specimens of B. musculus the bridge 

 completing the canal is arched forwards, where it joins the 

 posterior end of the condyloid cup, while in Megaptera the 

 anterior margin of the lamina is almost straight from the end 

 of the articular cup to the spine. The arching forwards is not 

 owing to greater thickness of the bridge in B. musculus, the 

 thickness being about the same (f inch) in Megaptera as in the 

 50-feet-long B. musculus. 



Spinous Process of the Atlas. There are marked differences 



