102 ME. "VV. H. FLOWER ON THE OSTEOLOGY OF 



ascending branches of the caudal artery, so characteristic of a certain region of the tail- 

 vertebra of the Cetacea, occur first in the fifth vertebra, but only on the left side ; in the 

 sixth they are seen on both sides, perforating the body of the bone, not the root of the 

 transverse process. 



As in all Cetacea, the caudal vertebrae suddenly change their characters at the point 

 where they enter the laterally expanded part of the tail and where the chevi-on bones 

 cease to be developed. They now lose their cylindrical form, and become broad, de- 

 pressed, and angular. There are seven such vertebrae in the present specimen ; and the 

 eighth from the end of the series, or the eleventh caudal, reckoning from the be- 

 ginning, is what may be called the transitional vertebra, being intermediate in form 

 and size between its two exceedingly difierent neighbours. The last two show a 

 rapid diminution in width. The terminal one is triangular in outline when seen from 

 above. 



Nothing can well be more dissimilar than the lumbo-caudal region of the spinal 

 column in Inia and Platanista. In the latter the short bodies, the long narrow trans- 

 verse processes, and high spines curving forwards and bearing immense laterally deve- 

 loped oblique processes with (throughout the lumbar region) well-marked anterior and 

 posterior articular surfaces, form most striking distinguishing characters. 



The chevron bones sent with the skeleton are ten in number. It is probable that 

 the first is wanting, as there is none corresponding with the form this usually has in 

 the Cetacea. I have therefore indicated its situation with a dotted outline in the figure 

 of the vertebral column (PI. XXV. fig. 2). These bones agree in general characters 

 with the processes of the vertebrae with which they are connected, being of moderate 

 length, very broad and rounded at their free extremity. The lateral halves of the last 

 three are not united in the middle line. 



There are thirteen pairs of ribs (PI. XXVII. fig. 2), the last being well developed 

 and articulating \vith the transverse processes of the corresponding vertebrae. They 

 are stout and heavy for their length, more so than in the ordinary Dolphins. In their 

 comparatively cylindrical form they present a marked contrast to the broad flat ribs of 

 Platanista. The last two or three are, however, much more compressed than the 

 others. The curve, very strong and angular in the first, gradually diminishes and 

 becomes more regular. The last has a slight turn outwards at the lower end, giving a 

 gentle sigmoid curve to the whole bone. 



The anterior ribs have long and broad, somewhat compressed capitular processes, 

 with distinct articular surfaces at the extremity and at the tubercle. In the fifth the 

 length of this process is sensibly diminished. In the sixth, seventh, and eighth it 

 shortens rapidly, the two articular surfaces being already confluent in the seventh. In 

 the ninth a rounded projection of the lower border of the vertebral end indicates the 

 rudimentary process ; in the tenth it has disappeared altogether, and henceforward the 

 upper end of the rib ends in a somewhat dilated, oval, convex, articular surface, gradu- 



