486 SCHULTE, SET WHALE. 



venous plexus turns ventrad and condensing to a large but short vertebral vein joins the superior 

 intercostal and the large spinal tap to form the posterior thoracic vein of Turner, which arches 

 over the dome of the pleura to the vena brachiocephalica. The confluence of these vessels occu- 

 pies the pyramidal space above the pleura and between the rectus anticus and scalenus muscles. 

 In the dorsal portion of this space, approximately at the level of the pleural dome projects the 

 neck of the second rib. This is crossed ventrally by the superior intercostal vein, which meets 

 the vertebral at its rostral border. The interval between the second rib and the costal process 

 of the fifth cervical vertebra, on account of the shortening of this region of the spine, is small and 

 is occupied in its entirety by the vertebral plexus as it turns ventrad to its debouchment, the 

 only other structures present being the vertebral artery and the very large stellate ganglion 

 of the sympathetic. Had the costal processes in this region persisted, the intervals between them 

 would have been entirely inadequate to the drainage of the plexus. Its presence therefore 

 seems to have modified the development of this region reducing and separating from the vertebra 

 the costal elements. In a sense this argument of room for drainage seems to be borne out by the 

 conditions in B. physeter as described and figured by Struthers, where the requisite space is gained, 

 not by the interruption but by t.he inclination rostrad of the costal processes. That of the sixth 

 cervical is in B. borealis only retarded in development, for it may form a complete arch in the 

 adult. That of the seventh is separated from its vertebra, losing its mesal segment, from 

 tubercle to capitellum while its remainder hypertrophies and fuses with the first thoracic rib. 

 This also has lost its proximal segment and articulates only with the transverse process. 



The spinous processes of the atlas and axis are of small size, in fact are little more than 

 tubercles; those of the remaining vertebrae increase in height caudad. They are compressed from 

 side to side, blunt and almost rectangular at their summits; none of them have a pointed profile. 

 On the transverse processes dorsally at a short distance laterad of the prezygapophyses are 

 very small conical processes, better marked on the more caudal vertebra?, which give origin, 

 to the trachelo-occipital muscle and supply points of attachment to the semispinalis capitis. 

 These processes are well shown in Andrews's figures of the adult vertebrae of this species. In 

 Struthers's illustration ' of B. physeter they appear on each side as a small tubercle, between 

 what he designates as the nerve groove stage and the tubercular stage of the transverse 

 process. 



The atlas is less massive in its build and more ringlike in form than that of the adult. This 

 depends upon the relatively smaller size of the lateral masses and the enlargement at their ex- 

 pense of the ventral portion of the neural canal embraced between them, which in the fcetus 

 exceeds in cross-section the region occupied by the spinal cord and its membranes. The sur- 

 faces of articulation with the occipital condyles converge ventrad extending well upon the 

 ventral arch where their extremities are separated by an interval of 2 mm. Their mesal margins 

 are distinctly concave and of a curvature almost concentric with that of their lateral margins. 

 Their extremities are rather pointed, their breadth far less than that of the condyles. Dorsally 

 at their junction with the dorsal arch there is a deep groove for the vertebral artery, and this 

 groove is not bridged over and converted into a foramen as in the adult. The spinous process 

 is reduced to a tubercle; the transverse process is very short, blunt and imperf orate. The 

 ventral arch increases in sagittal depth towards the midline and here its caudal margin protrudes 

 slightly beyond the body of the axis to give attachment to the longus colli. The articular sur- 



1 Struthers, F. Op. cit., pi. 2, fig. iv. 



