PEOFESSOE FLOAVEE ON THE EECENT ZIPHIOID WHALES. 



229 



As noticed by Van Beneden 1 in Mesoplodon sowerbyi, the bases of the transverse 

 processes of the hinder lumbar and caudal vertebrse are not perforated by vertical 

 vascular canals as in most Dolphins, but only the bodies of the posterior caudal vertebrse 

 (beginning at the tenth) have such perforations. 



There are nine chevron bones. The first consists of two pieces, not united in 

 the middle line. The fourth is the largest. Their principal characteristic is that 

 their spines are not particularly elongated downwards, but are large from before 

 backwards. 



The Ribs. — There are ten pairs of ribs, tolerably stout, especially thickening at their 

 lower ends, though somewhat contracted rather above the middle. 



The first is short and broad, articulating above by a well-developed tubercle with the 

 transverse process of the first thoracic vertebra, and by a short capitular process with 

 the body of the seventh cervical. It has a strongly pronounced angle. 



The second to the sixth gradually increase in length, and diminish in thickness; 

 afterwards they gradually become shorter. As far as the seventh inclusive, they have 

 all distinct tubercles articulating with the transverse processes, and well-developed 

 capitular process articulating with the hinder edge of the body or root of the arch of 

 the vertebra in front. After the fourth the angle becomes obscure and is lost in the 

 general convexity of the upper surface of the bone. In the eighth rib the tubercle is 

 rudimentary, and does not reach the much diminished upper transverse process of the 

 vertebra ; the head articulates with the hinder edge of the base of the pedicle of the 

 seventh vertebra, and on the right side only it has a small irregular articulation (not 

 found in any other case) with the anterior edge of the pedicle of the arch of the eighth 

 vertebra. 



The ninth rib wants the whole of that portion representing the head, neck, and 

 tubercle of the ribs in front, and has a truncated upper extremity, articulating to the 

 end of the large transverse process of the ninth thoracic vertebra. The tenth rib is 

 similarly articulated with the corresponding process of the tenth vertebra, and is nearly 

 as well developed as the one in front of it. 



The greatest length of each rib, in a straight line, is — 



First 



Second 



Third 



Fourth 



inches. 

 18 



26 



321 



37" 



Fifth 



Sixth 



Seventh 



inches. 



39 



39 



38| 



Eighth 



Ninth 



Tenth 



inches. 



38 



32 



29 





As in Physeter, Hyperoodon, and the other known Ziphioids, there are no 

 sternal ribs. 



The Sternum. — The sternum (PI. XXVII. fig. 3) is remarkably long and narrow. It 

 1 Loc. cit. p. 42. 



2l2 



