of the arch while on the other they proceed through the intervertebral 

 spaces. This order of alternation is gradually taken on beginning 

 with the thirteenth tail vertebra where the rib-carriers are lost. Each 

 successive nerve is on the one side pushed farther and farther ante- 

 riorly into the intervertebral space until about the nineteenth where 

 the exit is through the arch. This condition may help to throw some 

 light upon the occurrence of the unsymmetrical sacra as described by 

 G. H. Parkee in Necturus, Howes in Bombinator and Lucas 

 in Menopoma and Amphiuma. 



The vertebrae of the adult are much more complex than those 

 of the larva, supporting numerous processes for the attachment of 

 muscles as shown in my former paper (Journal of Morphology, Vol. IX). 

 On the ventral aspect of all the trunk vertebrae except the first is 

 seen a spine prominent anteriorly and diminishing posteriorly (Fig. 4 vp) 

 and also on either side of it small knob-like projections from the 

 anterior part of each vertebra. The haemal arches which were with 

 the exception of the first two closed ventrally in the larva are open 

 in the anterior half of the tail. Posteriorly the are closed and bear 

 two lateral processes on each side. 

 The neural spine not apparent in 

 the young is here well developed 

 (Fig. 4 np). The rib-carriers are 

 flattened dorso-ventrally except 

 those from the second to the 

 eighth which bear rudiments of 

 ribs. Those of the second and 

 third vertebrae are marked by 

 deep longitudinal furrows on the 

 anterior and posterior surfaces 

 thus making of the rib-carrier 

 two portions (Fig. 5). This divi- 

 sion was indicated in the larva 

 by a slight distal indentation 

 (Fig. 3 Fr). The distal ends of all 

 the rib-carriers of the trunk and 

 the first one of the tail are filled 

 with plugs of cartilage (Fig. 5 h). 



Fig. 4. Adult Amphiuma. Camera lucida drawing. Transverse section of the 

 fifth trunk vertebra anterior to its middle. Rib-carriers appear twice as long five sections 

 posterior to this, np neural spine; N neural arch; B-T rib-carrier; Art. v. arteria verte- 

 bralis; B basal stump ; vp ventral spine. 



:-rR-T 



