THE TRANSVERSE PROCESSES OF NECTURUS 557 



As Wilder pointed out, the distal ca\dty which contains the 

 dorsal cartilaginous process of the rib-bearer in the Uving state is 

 present in the second, third, and fourth vertebrae in Necturus, 

 and this connects with the dorsal head of the rib. 



In studjang cross-sections of the second vertebrae of a 70-mm. 

 larva, it was observed that the ventral cartilaginous rod of the 

 transverse process is located dorsad of the vertebral artery. In 

 the trunk vertebrae this element is ventrad of the same artery. 

 Figures 23 and 24 illustrate the morphology of this vertebrae. 

 The parapophysis (fig. 23, p.a.) extends a short distance laterad 

 from the notochord, but makes no connection with the rib- 

 bearer (r.6.) 



Two processes are seen developing caudolaterally from the rib- 

 bearer (figs. 23 and 24, d.p., v. -p.), and these connect with the 

 heads of the rib. This means that the capitular and tubercular 

 heads of the rib of the second vertebra are attached to out- 

 growths of the rib-bearer and the parapophysis takes no part in 

 this connection. 



This failure of the parapophyses to connect with the rib-bearer 

 may or may not be secondarj^ As was seen by the study of 

 younger stages, the parapophysis may be entirely suppressed. 

 In other cases it may be poorly developed and make no connec- 

 tion wdth the rib-bearer or it may connect only to be again sepa- 

 rated when bone begins to form. However, whether or not the 

 connection between these two elements is made, the rib is borne 

 upon outgrowths of the rib-bearer. 



If the macerated vertebral column of an adult Necturus be 

 examined (fig. 31), it will be observed that the transverse proc- 

 esses of the second and third vertebrae are higher than those 

 farther caudad. In tracing the ventral rod of the transverse 

 process of the second vertebra {v.p.) proximad, it will be seen to 

 extend dorsad of the foramen for the vertebral artery. In the 

 third vertebra it appears to be on the same level with this fora- 

 men, while in the fourth it extends below it. 



Although in the third vertebra the parapophysis in a greater 

 number of cases connects with the rib-bearer, here also the rib is 

 attached to outgrowths of the rib-bearer. In the fourth vertebra 



JOURNAL OF MORPHOLOQT, VOL. 36, NO. 4 



