548 D. L. GAMBLE 



The two processes which were seen just beginning to develop 

 forward from the dorsal portion of the neural arch in the 24-mm. 

 stage in the 26-mm. larva have continued their cephalic growth 

 until they meet the process developing caudad from the pre- 

 ceding vertebra. These will form the articular processes of the 

 definitive vertebra. The transverse process is in about the same 

 condition except that the rib-bearer has developed dorsocaudally 

 over the outer surface of the neural arch. In other words, 

 cartilage is forming in the inner edge of the transverse septum 

 along the line of its attachment to the neural arch. 



The cartilage of the rib now extends inward to the distal end 

 of the parapophysis, but procartilage still persists between these 

 two elements. After the fusion of the rib-bearer and the para- 

 pophysis, a lateral extension of the transverse process takes place 

 distad of this point. As the animal grows the rib attachment 

 must be shifted laterally to bring it into its final position. This 

 means that procartilage cells must persist between the trans- 

 verse process and the rib, so that proliferation of cartilage cells 

 may take place and the parapophysis grow laterally. It was in 

 a larva of about this age that Goeppert saw the rib-bearer ap- 

 pearing as a dorsal outgrowth from about the middle of the basal 

 stump. The study of younger stages shows that this is not the 

 case, but that the rib-bearer grows downward and fuses with the 

 distal end of the parapophysis and that the ventral head of the 

 rib is borne upon an extension of the parapophysis which develops 

 laterally after the rib-bearer has united with it. 



The rib gives off a dorsal process which becomes the tubercular 

 head. This extends dorsomesally toward the neural arch. In 

 the trunk region it never connects with a corresponding process 

 of the rib-bearer, but in the anterior region this does occur. 

 This will be discussed more in detail later. 



DEVELOPMENT OF ANTERIOR TRUNK VERTEBRAE 



As before stated, Goeppert's conclusions concerning the dorsal 

 shifting of the rib attachment in urodeles were based upon a 

 comparison of the conditions found in Necturus, Salamandra, and 

 Triton. After the study of a complete series of Necturus larvae, 



