THE TRUNK 



however, is affected by the fact that it is located above the longitudinal 

 body axis and by tension of the muscles that extend toward the head on 

 one hand and the tail on the other, and in life is slightly curved to a 

 greater or lesser degree depending on muscular differences and body 

 shape. 



The terminal epiphyses of the cetacean vertebrae are very distinct and 

 become thoroughly ossified into thin disks which fuse with the bodies 

 very late, especially in balaenid whales. Flower (1876) has stated that 

 whales appear to differ from all other mammals inasmuch as the neuro- 

 central suture is always placed a little above the junction of the arch 

 with the body. Anapophyses and postzygapophyses are absent as true 

 processes. Prezygapophyses may be well developed and present upon 

 all vertebrae, as in Mysticeti, Stenodelphis, Monodon, Mesoplodon, etc., 

 indicating that there is definite zygapophyseal articulation (at least by 

 ligaments) throughout the entire column ; or on the other hand they may 

 be totally absent from the central lumbar series, becoming gradually 

 differentiated craniad upon the first few lumbar and caudad on the last 

 few, or even entirely eliminated {Grampus griseus, figure 28). This 

 shows that in the area where they are not well defined zygapophyseal ar- 

 ticulations do not exist, which increases the limberness of the column by 

 just this much. Metapophyses are developed and in caudal sequence 

 gradually arise from low upon the neural arch to the base of the spinous 

 process. In the anterior thoracic series the di- and metapophyses usu- 

 ally occur unseparated, I believe, the diapophyses in most sorts of whales 

 gradually separating and descending from high on the arch to the cen- 

 trum, thus becoming parapophyses. In the Physeteridae, Kogidae, and 

 the Ziphiidae, however, there is a different condition, for the diapophyses 

 do not gradually change to parapophyses. On the contrary the former 

 diminish and disappear, while at the same time the latter become defined 

 well ventrad of the diapophyses and gradually increase in size. 



As previously remarked most cetologists refer to the phenomenal short- 

 ness of the whale's neck as though this character were entirely disasso- 

 ciated from thoracic conditions. As a matter of fact this shortening 

 process merely culminates in the neck, but also involves the anterior third 

 of the thorax. In mysticetes there is an almost insensible, gradually in- 

 creasing shortening of the centra from about the fifth thoracic to the 

 third cervical (in those sorts with fjee neck vertebrae) . In most por- 

 poises which have the posterior cervicals unfused these may be relatively 

 thinner, to a considerably greater extent than would be possible for any 

 thoracic vertebra bearing a rib. Consequently there is usually a more 



[177] 



