AUTHOR S ABSTRACT OF THIS PAPER ISSUED 

 BT THE BIBLIOGRAPHIC SERVICE, JXTLX 17 



THE ^MORPHOLOGY OF THE RIBS AND TRANSVERSE 

 PROCESSES IN NECTURUS MACULATUS^ 



D. L. GAMBLE 



THIRTY-ONE FIGURES 



A summary of the literature upon the transverse processes 

 and their relations to the ribs and haemal arches in the urodeles 

 results in contradictions with regard to the morphology of these 

 parts. An attempt to verify statements by a study of the 

 development of the parts concerned has resulted in the present 

 communication. Necturus was chosen as the type, partly for 

 convenience and partly because it was believed that it might 

 exhibit conditions primitive enough to serve as a basis for 

 interpreting the morphology of these structures in urodeles 

 generally. 



For a clear conception of the problem, the following observa- 

 tions are pertinent : the ribs of urodeles exhibit several differences 

 when compared with the dorsal fish ribs. In elasmobranchs the 

 ribs are connected with the centrum by means of the basal 

 stump, which is located ventrad of the vertebral artery. In 

 most urodeles, however, the ventral head of the rib is attached 

 to a process of the neural arch above the vertebral artery. If 

 this latter attachment were brought about by the simple dorsal 

 shifting of the rib and basal stump, the relations of the vertebral 

 artery in regard to these structures would be unchanged. 



Two interpretations of this condition obtain at present. One 

 is that, due to the dorsal shifting of the horizontal septum and with 

 it the rib, the latter structure has simply lost its connection with 

 the basal stump and has become attached to the neural arch 

 (Rabl, '92). 



' This problem was suggested by, and carried on under the direction of Dr. H. 

 D. Reed. The writer is not only indebted to him for liis help and advice through- 

 out the work, but also for the use of his splendid series of Necturus larvae. 



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