194 



NATURAL HISTORY OF BIRDS. 



their lower almost inter-thoracic portion, and their sudden concentration into the long 

 and thin tendons which run up the neck. The kink of the neck makes necessary a 

 special arrangement to prevent the tendon which runs along the posterior surface of 

 the neck from breaking away from the vertebral column when the muscle with which 

 it is associated contracts, and therefore a sling-band is found attached to the ninth 

 vertebra, through which the tendon passes, acting exactly in the same way as the 

 well-known sling-band in the knee region. 



m \ 



. 



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FIG. 93. Anhinga levaillanti, African darter. 



The alimentary canal of the darters is extremely peculiar, and has partly been 

 described in the introduction to this volume (p. 15). We may here add that the 

 African species has two small casca, while the American has only one. In both the 

 tongue is obsolete as an independent organ. It is very small in all Steganopods, but 

 in the others it is free at its anterior extremity, which is not the case in the darters, 

 the tongue of which is only indicated by a longitudinal groove and a slight transverse 

 ridge behind. 



