BY R. BROOM. 737 



process developed from the arch to which is articulated an in- 

 dependent additional element — an autogenous transverse process. 

 According to Flower* the transverse processes of the anterior 

 lumbar vertebrae of the pig are originally autogenous elements 

 though coalescing very early with the rest of the vertebra?, and 

 in certain cetaceans the transverse processes of the lumbar 

 vertebra? are autogenous elements. In many reptiles, and especi- 

 ally in those reptiles from which the mammals appear to have 

 sprung — the Theriodonts — all the trunk vertebrae have costal 

 elements, and in the lower trunk or lumbar region these elements 

 are articulated to the vertebra? exactly as are the autogenous 

 processes in the wombat. Fig. 4 represents the upper side of a 

 lower trunk vertebra of Cynognathus, and if this be compared 

 with the fourth lumbar of the wombat (fig. 3) it will be seen 

 that the two agree closely except in the different degree of 

 development of the parts, and that there is no reasonable doubt 

 but that the rib-like appendages of the vertebra of Cynognathus 

 are homologous with the autogenous transverse processes of the 

 vertebra of the wombat. 



Sacro-caudal Vertebra;. — In the human subject the term 

 " sacrum " is applied to the anchylosed five vertebrae which 

 support the pelvic bones. Here there is no difficulty in defining 

 the limits of the sacral series of vertebrae, and in many other 

 mammals the difficulty is no greater. There are many forms, 

 however, in which not only are a different number of vertebrae 

 anchylosed in different individuals, but where even in the one 

 individual the number increases as age advances. According to 

 Flower, " a more certain criterion is derived from the fact that 

 some of the anterior vertebrae of the sacral region have distinct 

 additional (pleurapophysial) centres of ossification, between the 

 body and the ilium. To these, perhaps, the term sacral ought 

 properly to be restricted, the remaining anchylosed vertebrae being- 

 called pseudo-sacral, as suggested by Gegenbaur." If this 

 criterion, however, be applied to the sacrum of the marsupials it 



W. H. Flower, " Osteology of the Mammalia. 



