124 PROFESSOR STRUTHERS. 



On separating the vertebrae, a fossa is seen on the posterior 

 aspect of each thickened part of the laminas, as if the anterior 

 edge of the lamina behind had passed into a cavity on the 

 lamina in front. On the 5th, on which these fossse are most 

 pronounced, they are elliptical, 2 inches transversely by ^ to | 

 inch in breadth, the broader end outwards, at about 1 inch 

 internal to the articular process, the narrow end 1 inch or less 

 from the spine ; depth, from ^ to |^ inch or less. They have a 

 very distinct and raised inferior margin, which is the true lower 

 edge of the under surface of the lamina, the fossa itself being 

 on the thickened posterior margin of the lamina. They have not 

 the appearance of having been covered by cartilage, but are evi- 

 dently parts into which something definite has been received. 

 On the 3rd, it is seen, on the less injured side, as a shallow 

 depression near the spine, 1 inch in length. On the 4th, they 

 have the length and breadth noted above on the 5th, but are 

 divided by a median ridge into an inner and outer part, as if two 

 parts of the lamina behind had been lodged in them. On the 

 6th, it is seen on the least injured side, as if divided into three 

 parts. If the corresponding part is represented on the 7th 

 vertebra, it is as a rough depression running along the posterior 

 margin of the lamina, beginning at the articular process, seen on 

 the upper aspect of the posterior margin of the lamina. So far as 

 they are complete, there is no special thickening, or mark, on the 

 anterior edge of the lamina behind corresponding to these fossee. 



[Ill the B. 7nusculus there are spaces on each side of the 7th and 

 6th arches, wide enough to receive the hand flat, and a narrower one 

 between the 5th and 4th. The laminae are flat and thin compared 

 with those of Megaptera, the anterior border of the 3rd, 4th, and 

 5th so thin as to be flexible. The laminae are not nearly so thin as 

 in the 65 to 66-feet-long B. musculus, but are thinner than in the 64- 

 feet-long B. miisculus before described {loc. cif., 1872). Nor are the 

 very marked anapophysial processes described in them present in 

 this 50-feet-long B. musculus to any great extent. They are seen 

 only on the 3rd and 4th vertebrae, wdth a mere trace on the 5th, and 

 are short and flat. The fossa; seen on the posterior border of the 

 laminae in Megaptera are not present in this 50-feet-long B. mus- 

 culus, but corresponding fossae or grooves are seen, more or less, in 

 the three more mature individuals, best marked in the 64-feet-long 

 one, least marked in the 60i^-feet-long one. They are not so 

 sharply marked on their inferior border as in Megaptera, and lie 

 more towards the spinous process. 



