562 



D. L. GAMBLE 



arch (fig. 30A) . Posteriorly the rib is on a level with the middle 

 of the centrum (fig. 29A) . 



6. The parapophyses of the vertebrae in which the ribs are 

 high do not he in a horizontal plane, as they do farther back in 

 the trunk, but extend dorsolaterally and approach the rib-bearer 



Fig. 29 Series of diagrams to illustrate the morphology of the ribs and trans- 

 verse processes in the trunk region of Necturus. c.h., capitular head of rib; 

 t.h., tubercular head of rib; black, rib-bearer; stippled, parapophysis and 

 haemapophysis; white, rib. A, B, and C represent successive stages in the devel- 

 opment of these structures. D, E, and F show the successively less differentiated 

 condition encountered in passing toward the tail in a larva in which the transverse 

 processes of the anterior vertebrae are at a stage similar to that represented by B. 



end to end (fig. 30A) . In this anterior region the rib-bearer and 

 parapophysis do not fuse until relatively late, while the rib 

 becomes attached to the rib-bearer before rib-bearer and para- 

 pophysis come together (fig. 30 A, B, C). 



7. In the second and third vertebrae the capitular as well as 

 the tubercular heads of the rib attach to corresponding proc- 

 esses of the rib-bearer. In these vertebrae the parapophysis 



