488 



SCHULTE, SEI WHALE. 



The fourth rib has a rudimentary neck and head, which fails to reach the vertebrae. The 

 remaining ribs lack these parts and articulate by their proximal extremities with the trans- 

 verse processes. The lengths of the ribs are given in the following table. Tne measurements 

 were taken with callipers from end to end. 



1. 



2 



3. 



4. 



5. 



6. 



7. 



8. 



9. 

 10. 

 11. 

 12. 

 13. 



mm. 

 30 

 45 

 50.5 

 52.5 

 54.5 

 57.5 

 60.5 

 58 

 54.5 

 51. 

 46. 

 45. 

 35. 



The first rib, as has been said, is bicipital, a cervical rib being fused with its rostral aspect. 

 A narrow cleft, diminishing ventrad, separates the two portions as they approach the spine, 



this interval has a length of 12 mm. It is 

 filled with muscle of the same orientation and 

 continuous with the scalenus. The cervical 

 rib expands proximad, becoming flattened 

 rostro-caudad and articulating with the trans- 

 verse process (dorsal bar) of the seventh cervi- 

 cal vertebra. Ventrally it is connected with 

 the transverse process of the fifth cervical by 

 ligament. The proximal extremity of the first 

 thoracic rib is also flattened and expanded. 

 It articulates with the transverse process of the 

 first thoracic vertebra. In both, the head and 

 neck are wanting. The condition is identical 

 upon the two sides. 



That the additional element in this fused 

 rib is a cervical rib is shown not only by its 

 topography and connections, but also by the 

 absence of the ventral bar (costal process) of 

 the transverse process of the seventh cervical vertebra. 



While the morphology of the two-headed rib presents no especial difficulties, its taxonomic 

 value has been the subject of much discussion. 1 It has been argued that as the cervical rib in 

 man is a variant, so it is also in Balcenoptera borealis, an argument evidently wrong in principle, 

 for the question of normal vs. variant in a species must be answered by establishing with a 



Fig. 8. Sternum and first rib. 1, Sternum. 2, Cervical rib. 

 3, First thoracic rib. 4, Sternohyoid. 5, Sternomastoid. 6, 

 Sternomandibularis. 7, Pectoralis. 8, Rectus. 9, Obliquus ext. 

 10, Scalenus. 



1 Turner, W. On the so-called two-headed ribs in whales and man. Jour. Anat. and Phys., Vol. 5, 1870-1871, p. 349. This article 

 is useful for the older literature. Also, by the same author, the transverse processes of the seventh cervical vertebra in Balcenoptera 

 Sibaldii. Jour. Anat. and Phys., Vol. 5, p. '382. The so-called two-headed ribs in whales and man. Jour. Anat. and Phys., Vol. 6. 

 p. 445. Cervical ribs and so-called bicipital ribs in man, in relation to corresponding structures in the Cetacea. Jour. Anat. and Phys., 

 Vol. 17, p. 384. 



