11 



body to the rib-carrier (Fig. 2), is replaced by a lamina of bone, the 

 basal stump (Fig. 4, 6 and 7 B) which is expanded horizontally at 

 the proximal portion so as to be attached along almost the entire 

 length of the vertebral body. Between the rib-carrier and the basal 

 stump courses the arteria vertebralis. The lower surface of the basal 

 stump at its origin is almost on a level with the ventral surface of 

 the vertebral body. This process on the sacral vertebra is more 

 strongly developed but does not reach the ilium. The basal stump 

 is also present on the vertebrae in the anterior half of the tail (Fig. 6). 



These are the vertebrae which in the larva bore rib-carriers. 

 The ribs in the anterior part of the trunk are of the same number, 

 same shape and proportionally of the same size as in the larva. 

 The second rib terminates in a cartilaginous plate similar to that 

 described by Mr. Iversen for Salamandra atra (Anatomischer 

 Anzeiger, 1889). The hole in the plate is proportionally smaller than 

 in the larva. The ribs are well ossified. The first and second are 

 apparently double, a cross section at the proximal end presenting 

 much the same appearance as figure 5. The dorsal part distally be- 

 comes weaker and ends in an attachment of fibrous tissue to the 

 stronger ventral part, thereby indicating that it is the dorsal rib pro- 

 cess as described by Göppert in the sacral rib of Menobranchus. 

 The condition of the first an second ribs in the young Amphiuma 

 clearly shows that the dorsal rib-process is produced by a longitudinal 

 splitting of the original rib material and therefore is not homologous 

 to the dorsal rib-process (dorsaleRippenspange) as represented 

 by GÖPPERT in the anterior vertebrae of Menobranchus. No 

 evidence of a double character appears in the five posterior ribs the 

 latter of which is so short as to be scarcely distinguishable. 



Although the intervertebral spaces are wide, the spinal nerves in 

 the terminal half of the tail make their exit through foramina in 

 the middle of the arches and are not alternate as found in the larva 

 but quite opposite. 



From the above exposition of facts it is apparent that Am- 

 phiuma has in its vertebral column the primitive selachian conditions 

 in a much less degree than according to Göppert characterize Meno- 

 branchus and Salamandre larva. The traces of the basal stump 

 are present in all the trunk and anterior tail vertebrae only as a 

 fibrous band extending from the ventral side of the vertebral body 

 to the distal end of the rib- carrier. Since in the adult animal this 

 band ossifies its identity with the basal stump is evident not only 

 from the location but also from the presence of the vertebral artery 



