VARIATION IN TOAD AND ISOPOD. 



271 



sixth, seventh, and eight vertebrae are of nearly equal size, the united 

 centra of this abnormal specimen are only very slightly longer than that of 

 the sixth, which is normal. The transverse processes of the two vertebrae 

 are completely separate, but are close together, and are of normal lengths. 

 The intervertebral foramina between the fused vertebrae are in all respects 

 similar on both sides, and are much smaller than in the normal skeleton. 

 Whereas in normal specimens, the foramen in this region is formed by the 

 arching in of the anterior border of the pedicle of the neural arch below 

 the anterior zygapophysis, it is formed in this case almost equally by the 

 pedicles of the two vertebrae, or on the left side perhaps more by that of the 

 seventh vertebra. The foramina are, moreover, very small, being narrower 

 from before backwards, and also much more constricted dorso-ventrally ; on 

 the whole they are only about one-fourth as large as in the normal skeleton. 



Cases of the fusion of the posterior vertebrae have been described by 

 Howes ['93, p. 268] and Adolphi ['92 and '93]. 



As this abnormality has apparently to do with the sacrum, its probable 

 significance will be treated of together with the following cases. 



Case 3. Bufo vulgaris, $ . Sacrum formed by the ninth vertebra 

 07i the right side, and by the ninth and tenth on the left. (Cut. 3.) 



The ninth vertebra preserves the essential characteristics of the sacrum, 

 but is deficient in some respects. The 

 centrum presents two articular facets on its rs**»«»-7 



posterior surface, as in the normal example ; 

 the transverse process of the right side is 

 of normal size and shape, but that of the 

 left is much smaller and somewhat shorter 

 and slightly thicker ; the anterior and the 

 left posterior zygapophyses are normal, but 

 the right posterior one is represented only 

 by a short spiniform process, which does 

 not articulate at all, there being left an 

 empty space between it and the correspond- 

 ing anterior end of the tenth vertebra. 



Cut 3. 



