AXIAL SKELETON OF THE OSTRICH. 427 



The Fortieth Vertebra. 



This has the transverse and spinous processes less developed, and the former have a 

 rather more dorsal origin (figs. 59, 60, & 61, 12). 



The median notch of the neural arch is more marked (fig. 61, 12). 



The centrum is more excavated, causing each lateral margin of its ventral surface to 

 be more concave. 



The Foety-fikst Vertebra. 

 The difierences just noted are here intensified (fig. 62, 41). 



The under surface of the centrum begins to exhibit antero-posteriorly directed exca- 

 vations of its substance. 



LATERAL ASPECT OF THE VERTEBRA FROM THE FORTIETH TO THE FORTY-SIXTH 



INCLUSIVE IN AN IMMATURE CONDITION (natural size). 



Fis. 62. 



41 



d, diapophyses ; ?is, neural spines ; p, parapophj'ses ; t, transverse processes, including the undifferentiated 



parapophyses and diapophyses. 



The Fokty-second Vertebra. 

 Again we find an intensification of the same characters ; but, in addition, the root of 

 each transverse process sends out a minute process on its ventral origin, i. e. a jjara- 

 pophysis (fig. 62, 42, p). 



The Forty-third and Forty fourth Vertebra. 

 With progressive diminution of the other process, the parapophyds is here rather 

 more prominent (fig. 62, 43 & 44). 



The ventral surface of the centrum is more excavated. 



The Forty'-fifth and Forty-sixth Vertebra. 

 These vertebrae are like the two last noticed, but are smaller, and have the diapo- 

 physis projecting preaxially and more decidedly separated from the more marked para- 

 pophyses, which latter project outwards, one from each lateral margin of each centrum, 

 while the ventral surface of each centrum is deeply excavated antero-posteriorly on each 

 side of a median antero-posterior lamella (fig. 62, 45&46). 



3o2 



