279 



Specimen A. Chiefly conspicuous by the presence of a 

 supernumerary (tenth) vertebra. The anterior seven vertebrae departed 

 from the normal condition only in respect to the transverse processes 

 of the second one, which were rotated unusually far forwards. The 

 ninth vertebra was concave in front (Fig. 2) instead of being convex as 

 usual, and accordingly the eighth, which is normally biconcave, resem- 

 bled those in front of it in being procoelous. The posterior faces 

 of both the ninth and tenth were doubly convex (Fig. 3 and 4) like the 

 normal sacral - vertebra, the front face of the tenth being of necessity 

 doubly concave. The urostyle was normal, the apertures of exit for 

 the last pair of spinal nerves being well developed. Fig. 5 s. 10. 



The characters of the sacrum were remarkable. The ninth ver- 

 tebra was asymmetrical; on the right side it bore the familiar sacral 

 transverse - process but no posterior zygapophysis ; while on the left 

 the transverse - process was short as that of the eighth, the zygapo- 

 physis being enormously enlarged so as to form a powerful articu 

 lation with that of the vertebra behind. The transverse processes of 

 the tenth vertebra were at their maximum of development, furnish- 

 ing the main articulation for the hip girdle; they were however 

 asymmetrical, that of the left side being expanded distally and much 

 the more powerful of the two. There were thus two sacral vertebrae 

 present, the anterior of which had failed to establish its connection 

 with the left half of the hip girdle ; neither vertebra had the anterior 

 convex -face so characteristic of the normal sacrum, but seeing that 

 that structure is occasionally procoelous, it is clear that the anterior 

 of the two must have been the true sacral - vertebra. Bourne has de- 

 scribed i) a Frog in which ten vertebrae were similarly present; the 

 superadded one (the tenth of the series) however remained simple and 

 destitute of connection with the hip girdle, and it is remarkable that in 

 his specimen as in my own the posterior zygapophysis should have 

 been suppressed on one side and correspondingly enlarged on the 

 other. The side on which the enlargement took place was reversed 

 in the two cases, and the modification must have been due to dififerent 

 causes in each. Bourne holds the reappearance of the tenth ver- 

 tebra to be reversionary to the Urodele condition; granted that as a 

 means of accounting for the presence of the structure, it is no less 

 clear that the characters of it in the specimen now under consideration 

 can be definitely associated with the physiological requirements of the case. 

 The place of the true sacral vertebra was usurped by the new comer; 



1) 1. c. p. 87—8. 



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