76 PROFESSOR STRUTHERS. 



may be recognised the lower stage, piercing the haemal ridge ; 

 the middle stage, piercing the body internal to the transverse 

 process, showing lower and upper foramen ; and the upper stage, 

 piercing the neural arch. The study of the changing position 

 of these great apertures in the transition from the three-per- 

 foration condition to the simple condition behind, is the more 

 interesting as they form characters by which these vertebrae of 

 Megaptera may be distinguished from those of B. musculus and 

 B. borealis. These are great apertures, all large enough to 

 admit the point of a finger. They diminish upwards. While 

 within the bone, the passage communicates laterally with the 

 exterior by a system of apertures seen on the side of the bodies. 



The lower stage exists only on the 7th and 8th, as the per- 

 foration in the haamal ridge, large enough to admit a large 

 finger. Behind the 8th, the passages pierce the roof of the 

 haamal groove, and become at once concealed in the bone. 



The middle or lateral stage of the vertical passage exists 

 from the 6th caudal vertebra backwards. On the fifth, it has 

 run out into the deep notch bounding the transverse process 

 anteriorly. The deepest part of this notch, on the right side, is 

 marked by traces of the passage, and a wide groove passes up 

 from the notch on both sides. On the sixth, it is a canal, 

 1J inch in length, in the side of the body, 1 to 1J inch internal 

 to the transverse process. Between the notch and the foramen 

 there is an interval, 2 inches on the right side, f inch less on 

 the left side, and the notch is to the extent of that difference 

 deeper on the left than on the right side. The sixth is the last 

 vertebra with a projecting transverse process. On the seventh 

 this stage of the passage is 4 inches in length within the bone, 

 the lower aperture half-way below, the upper aperture less than 

 half-way above the transverse process. From the upper aper- 

 tures of the 6th and 7th, broad, well-marked grooves are seen 

 to pass up to the neural perforation or notch. These grooves 

 appear to have had a membranous roofing, at least at their 

 lower part. On the eighth, the middle stage is now roofed over 

 along nearly the whole side of the body, beginning to be so 

 immediately after the perforation of the hasmal ridge, leaving 

 only a large window between, and reaching up to within 1 inch 

 from the neural perforation. Behind the eighth, the passage 



