100 PllOFESSOR STRUTHERS. 



tera. On the 7th, over the middle of the costal fossa, the margin is 

 ^ inch thick. On the 12th, 13th, and 14th they are narrow ellipti- 

 cal facets, very shallow ; on the 13th and 14th quite on the end of 

 the process and looking straight ontwards. The transverse pi'ocess 

 of the 1 5th bears no mark for its rib, and is very little thicker than 

 that of the first lumbar. The anterior half or two-thirds of the fossa? 

 have been covered with cartilage ; when the 12th is reached the whole 

 area has been so. This contrasts with Megaptera in which the fossae 

 do not present the appearance of having been covered by cartilage. 



25. Lumbo-Caudal Transverse Processes in B. musculus. — Origin. 

 — Like the hinder dorsal, they are on a line with about the middle 

 of the bodies. They spring nearer the front than the back of the 

 bodies, a little on the 1st lumbar, increasing in this respect back to 

 the 11th ; less so on the three next ; on the 15th rather the reverse ; 

 from the 1st caudal to the 6th, decidedly nearer the back of the 

 body, this being due to the greatly increased depth of the anterior 

 concavity after the vertical foramen has opened into it. After the 

 7th caudal, in which that foramen pierces the process, the process 

 springs much nearer the front than the back of the body. 



The forward directio7i begins with the 3rd lumbar, and increases to 

 the 7th. From the 10th the forward direction lessens, and at the 15th 

 is very slight. On the first six caudal the processes are on the whole 

 horizontal, varying a little according as the anterior or posterior 

 corners are most developed. Behind the 6th the direction of the 

 processes is noted with their form. In length, they diminish a little 

 from the 1st to the 10th lumbar, and from the 11th rapidly backwards. 

 The thickness is about half that of the dorsal processes. In breadth, 

 they vary little from the 1st lumbar to the 3rd cavidal, averaging 

 about 6i inches; the 13th and 15th lumbar have the exceptional 

 breadth of 7 inches. The regained breadth of the 7th caudal, and of 

 the three or four behind it, is owing to the change of form conse- 

 cpient on the vertical foramen. 



Form. — The lumbo-caudal processes, back to the 6th caudal, pre- 

 sent the same flattened and outwardly expanded form as the posterior 

 dorsal processes, but are thinner all along the process. Back to the 

 12th lumbar the wing is less square-shaped, as the expansion is less 

 and also more gradual. The distinction between neck and wing is 

 less marked, but the anterior interti-ans verse projection is recognis- 

 able, and the projection on the posterior border is rather better 

 marked than on the dorsal processes. Behind the 12th, the lumbar 

 processes become more convex externally from the rounding off of the 

 angles. The first six caudal shovi^ this degeneration to a greater 

 ■ extent ; the neck shortens, and the wing-stage is represented only by 

 a semicircular end beyond the anterior and posterior intertransverse 

 projections. The anterior concavity of the neck deepens, and on the 

 7th caudal, is enclosed, forming the foramen of the vertical passage. 

 The stunted processes behind this, having the foramina, are very 

 bi'oad, springing now from as far forward as where the body joins its 

 epiphysis. Behind the 8th, however, the foramen is at or behind 

 the middle of the process. 



