THE TRANSVERSE PROCESSES OF NECTURUS 565 



5. The distal excavation which Goeppert did not observe in 

 the dorsal part of the transverse process of Necturus is present 

 in the second, third, and fourth vertebrae. This has already been 

 pointed out by Wilder. Therefore, in these vertebrae the carti- 

 laginous tubercular head of the rib is attached to an outgrowth 

 of the rib-bearer. In the remaining trunk vertebrae this con- 

 nection is not made. 



6. The ventral cartilaginous rods of the transverse processes 

 in the second and third vertebrae are not homologous with those 

 of the other trunk vertebrae. This ventral rod in these two verte- 

 brae is an outgrowth of the rib-bearer, dorsad of the vertebral 

 artery and bears the capitular head of the rib. The ventral rod 

 of the transverse process in the remaining trunk vertebrae repre- 

 sents an elongation of the parapophysis which passes ventrad 

 of the vertebral artery. 



7. The relation of the transverse process and rib heads of the 

 second and third trunk vertebrae in Necturus is exactly similar 

 to the condition throughout the trunk in Amblystoma and 

 Salamandra. 



8. The primitive basal stump (Gadow's basiventral element) 

 develops a lateral process, the parapophysis, and a ventral, the 

 haemapophysis. In the trunk region of a younger stage, both 

 are present. In some vertebrae these are joined and in others 

 are separated. This separation is secondary. In the trunk the 

 parapophyses persist and are connected with the ventral head of 

 the rib. The haemapophyses here disappear, while in the tail 

 region they elongate to form the haemal arch and the para- 

 pophyses disappear. 



9. In conclusion, therefore, it may be said that the change in 

 attacliment of the rib, from the centrum to the neural arch in 

 urodeles, is not the compUcated process that Goeppert thought. 

 The capitular head of the rib does not remain attached to the 

 basal stump or vestige of it, but loses its connection with the 

 parapophysis and joins with the rib-bearer (compare figs. 29 and 

 30) . This change in rib attachment is correlated with the dorsal 

 shifting of the horizontal septum. 



