110 PROFESSOR STRUTHERS. 



mnsculus. All round its upper, outer, and inferior margins the 

 area is defined by the sharp edges of the articular surfaces. 

 The sharp edge crosses the upper end of the furrow between 

 the mesial and lateral articular surfaces, and the surface of the 

 furrow resembles that of the articular surfaces, not that of the 

 ligamentous area. The surface of the area is undulating and 

 rough, excavated along the outer half, deeply pitted at the 

 superior external angle, especially on the left side, less irregular 

 but more rough along its inner half. Internally it is bounded 

 by a sharp edge where it meets, at a right angle, the narrow 

 surface bounding the canal. In the specimens of B. musculus 

 this angle is rounded off. 



The great lateral articular surfaces present less general 

 convexity than in any of my five specimens of B. musculus. 

 Internally the surface is encroached on by the ligamentous area, 

 and on the outer half it is either nearly flat or a little concave 

 transversely. In the specimens of B. musculus the surface has 

 a marked transverse convexity, with a little concavity towards 

 the outer part near the raised outer edge. Instead of the more 

 or less raised articular surface, bounded by a sharp edge, seen in 

 B. musculus, the upper half of the articular surface in Megap- 

 tera is, as it were, scooped out to the level of the concave 

 posterior surface of the transverse process. The less convexity 

 of the surface, together with the greater ligamentous area, in 

 Megaptera would seem to indicate adaptation to less movement 

 between the atlas and axis and more firm binding of these two 

 vertebrae together in it than in B. musculus. 



Canal of the Atlas. — The canal presents some differences 

 from that of B. musculus. The height (7^ inches) is less than 

 in any of the five specimens of B. musculus (7f to 8 inches) ; in 

 the 50-feet-long B. musculus almost 8. This is probably owing 

 to the height of the inferior arch (3f inches on the anterior 

 aspect), which is about f inch greater in Megaptera than in the 

 50-feet-long B. musculus. The lower end of the canal has thus 

 a less pointed form than in B. musculus. The lower, or odontoid, 

 part of the canal, marked otf from the neural part by the con- 

 striction, varies a good deal in breadth in the different specimens 

 of B. musculus. Especially in two of the specimens previously 

 noted {loc. cit., 1872) this part of the canal is much narrower 



