90 PROFESSOR STRUTHERS. 



there is a thick prominent mesial ridge about the size of a little 

 finger, but prismatic. It is less marked on the 4th and 5th 

 caudal. Forwards, it is only slightly present in several of the 

 posterior lumbar vertebrae, and re-appears on the posterior half 

 of the dorsal region as a low convexity. 



[In B. musculus this mesial ridge is very faintly and variably pre- 

 sent on some of the lumbar vertebrse.] 



The bifurcation of the posterior border of the spinous process 

 is quite peculiar on 3rd, 4th, and 5th dorsal. It begins near the 

 top of the spine and the included space, half-way down, is 

 nearly 1 inch broad, grooved and with a low median ridge. 

 The difference behind the 5th dorsal is owing to the develop- 

 ment of this low median ridge as the posterior border of the 

 process, and to the partial filling up of the groove on each side 

 of it. 



[In B. musculus, the posterior articular processes, back to the 10th 

 dorsal, project far enough to be opposite about the upper and anterior 

 third of the minor anterior processes ; more forwards, less as we go 

 back. In the lumbar region the distance between them, antero- 

 posteriorly, increases to about 1 inch. If the posterior processes 

 move straight back, in extension, to that extent, they must go be- 

 tween the minor anterior processes, but they will not touch, as the 

 distance between the latter is considerably greater than that between 

 the two posterior articular processes. The above mentioned character 

 of the 3rd, 4th, and 5th dorsal spines in Megaptera is not seen in B. 

 musculus, in which the posterior edges of all the spines are thin and 

 projecting.] 



17. HOMOLOGY AND ADAPTATION OF THE ARTICULAR PRO- 

 CESSES. The internal anterior articular processes may be looked 

 on as the true zygomal processes, the great anterior processes 

 rather as metapophyses. Behind the articulation between the 

 5th and 6th dorsal there is no appearance of the part having 

 been covered by cartilage, but dissection alone can determine 

 that. After that articulation the processes cease to be in con- 

 tact, the interval increasing from J inch rapidly to f inch, 

 laterally, as we go back. With this distance between them, 

 laterally, the anterior and posterior processes could not come in 

 contact without more rotation on the axis of the bodies than the 

 intervertebral discs are likely to allow. At the posterior lumbar 

 and the caudal regions they could not even approach each other 

 antero -posteriorly except during severe extension. 



