PLATANISTA. 547 



and lying at a considerably lower level below the metapophyses than in the 

 preceding vertebra and conJB.ned to a small surface, which is concave in the adult 

 and situated on the outer basal border of the pedicle. The disappearance of the 

 superior transverse process in the thoracic region is very gradual, and is completed 

 in the seventh vertebra, where the rib-bearing process is wholly central. In the 

 succeeding vertebrae, the process is very rudimentary, but it increases in lateral 

 extension to the ninth. In all of these, it is an exogenous product of the centrum, 

 and thus differs in its development from the superior transverse processes of the 

 neck. When there are ten ribs the last is generally articulated to two transverse pro- 

 cesses by its head to the autogenous transverse process of the tenth vertebra, and by its 

 angle to the much larger similar transverse process of the first lumbar vertebra. In 

 the third skeleton already referred to, the neurocentral suture is intact in all the 

 dorsal vertebrae, save the last, in which, and in aU the remaining neural arches, it has 

 amalgamated with its centrum, although the remains of it can be traced in the 

 last dorsal, in all the lumbar vertebrae, and in the first three caudals, its 

 union with the centra being most complete in the terminal six caudal vertebrae. 

 The transverse processes of the lumbar region are also autogenous products, and in 

 the younger skeleton they are all ossified, but quite distinct at their bases from the 

 centra, and broadly tipped with cartilage. The neural arch is even at a still higher 

 level on the bodies than in the last dorsal vertebra, and they are quite distinct from 

 each other, none of them articulating by zygapophyses. The metapophyses are 

 short and abruptly truncated, their tips being cartilaginous. The laminae are also 

 separated by a cartilaginous interspace. In the older foetus, the neurocentral suture 

 is intact, as are also all the sutures at the bases of the transverse processes, which 

 in the case of the first to the fourth lumbar disappear at a later period than all 

 the others, and then the neurocentral, as illustrated by the condition of these 

 parts in the third and oldest skeleton. In the former, or second skeleton, the 

 metapophyses are strongly developed and overlap the vertebrae, and the zyg- 

 apophyses are perfect. 



In the caudal region, only the first transverse processes are ossified, but a small 

 ossicle can be detected in the fourth and fifth ; all the remaining processes are 

 wholly cartilaginous. The third transverse process, on either side, has the remarkable 

 character, that it is developed from two ossific centres, the one next the centrum being 

 the larger and the distal one the smaller. In the right side, the ossicles are perfectly 

 distinct, whereas on the left, in which they are much more developed, they have 

 partially united. This arrangement exactly simulates the condition of things 

 found in the last dorsal vertebra, in which the rib is developed at the extremity 

 of its autogenous transverse process. The ossicles of the chevron bones are 

 developed as far back as the fourteenth in the youngest specimen, but in the 

 third and oldest skeleton they can only be traced the same distance ; it is evident, 

 therefore, that all the remaining chevrons are developments of after-life, as the 

 mother of the former specimen had twenty -two such structures. The ossicles 

 occur as little round plates on the sides of the cartilaginous arches. The neural 



