144 



PROFESSOR STRUTHERS. 



proper. The seventh shows exceptional narrowness of the 

 articular surfaces (breadth, 1^ inch ; breadth of sixth, 2 inches ; 

 of eighth, If inch), with consequent thinning of the lamina; 

 and much greater width of the arch than in the sixth. This is 

 the chevron bone belonging to the first vertebra, in which the 

 anterior and posterior hasmal tubercles meet to form a con- 

 tinuous ridge. 



[The corresponding chevron bone in B. mnsctdus (the 12th) is 

 that on which the articular surface begins to diminish to a marked 

 extent in breadth, but the narrowness is continued on the chevron 

 behind it.] 



41. Table VIII. — Measurements of the Chevron Bones of 

 Megaptera, and of the Mh Chevron Bone of B. musculus, 

 in inches. 



42. EXPLANATION OF PLATE VI. 



Fig. 17. Posterior aspect of atlas of Megaptera longimana, reduced 

 to ^. a, a, the lateral articular surfaces ; b, mesial articular surface ; 

 c, ligamentous area. The form of the spinal canal, its neural and 

 odontoid parts, is seen. Compare with this figiu'e the figure show- 

 ing the same aspect of the atlas of B. musculus, with the transverse 

 ligament, in this Jour?iaI., vol. vii., 1872, fig. 5. In Megajjtera ob- 

 serve especially the quadrate form of the ligamentous area, and the 

 presence of a mesial ai'ticular surface sej^arating the lateral articular 

 surfaces below. The difference between the right and left shallow 

 groove between the lateral and mesial articular siu-faces is seen in 

 the figure. The small surface seen below the mesial articular surface, 

 on the subaxial peak of the atlas, is not articular. The very slight 

 projection of the lateral articular surfaces at the transverse processes 

 is seen in the figure. 



Fig. 18. Sternum and first pair of ribs of Megaptera longimana, 

 seen from before, reduced to ^.,. a, a, the roixgh part on the inner 



