ANATOMY OF .MEGAPTERA LONGIMANA. 109 



subaxial peak, here J inch in length, which meets it at nearly 

 a right angle. This aspect of the subaxial peak has somewhat 

 the appearance of having on it an articular facet the size of the 

 end of a finger, but there is no corresponding facet on the axis. 



The mesial articular surface is separated from the great semi- 

 lunar lateral surface by a furrow J to f inch in breadth ; in 

 length 1| inch on the right side, f inch on the left. Although 

 the separation of the mesial surface is very marked on the 

 macerated bone, it does not follow that it was separated by 

 ligament, or even that the articular cartilage was not continuous 

 with that on the lateral surfaces. The floor of the furrow is not 

 rough, and the levels of the surfaces on either side are nearly 

 the same, the surface on the outer side of the furrow a little 

 more projecting. 1 



(6) The ligamentous area, for the attachment of the great 

 interosseous ligament on each side between the atlas and axis, 

 crescentic in form in all the specimens of B. musculus, is quadrate 

 or rhomboidal in Megaptera ; also much broader, and altogether 

 considerably larger than in B. musculus (see fig. 17, and, for 

 comparison, fig. 5, Plate II., loc. cit, 1872, showing the form in 

 B. musculus, and also the transverse ligament). In Megaptera 

 the length of the area averages 3J inches, breadth about 2J, at 

 its lower part 2 inches. The greater breadth and quadrate 

 form in Megaptera are gained above by its throwing out a 

 superior external angle, prolonged like the point of a finger ; 

 below, by its extending as an inferior external angle between 

 the mesial and lateral articular surfaces ; and internally by the 

 boundary of the canal being less curved outwards than in B. 



1 Professor Flower has described (Proc. Zool. Soc., 1864, p. 402), on the atlas of 

 the fin-whale in the Leyden Museum, taken on the north-west coast of Java, 

 the lateral articular surfaces as not confluent below, but having between them "a 

 distinct, oval, transversely elongated facet, and another smaller round one is 

 situated on the upper surface of a pointed triangular projection from the hinder 

 border of the inferior surface of the bone, which runs under the body of the axis." 

 Also corresponding surfaces on the axis. The interval, shown in his figure (fig. 

 12) of the axis, between the median facet and the great lateral surface is consider- 

 able. In rny B. borealis the two lateral surfaces are confluent, as in B. musculus, 

 and there is no articular facet on the subaxial peak. In iny figure of the posterior 

 surface of the atlas of B. musculus (loc. cit, 1872, fig. v.) a narrow median furrow 

 is seen separating the great lateral articular surfaces, but reasons are given (loc. 

 cit., pp. 15 and 50) for not regarding that as implying non-continuity of the 

 articular cartilage. 



