OCT. 1895. VERTEBRAL COLUMN OF AMIA HAY 9 



forward somewhat over the hinder border of the pleurocentrum in 

 front, while the hinder border of its own hypocentrum is left 

 somewhat uncovered. As we move forward we find the neural bases 

 shifted gradually backward, so that in the case of the most anterior 

 free intercentrum the upper arch reposes on its upper surface, extend- 

 ing neither on the pleurocentrum in front nor on that behind. In 

 the hinder dorsal region we find that the neural bases are set still fur- 

 ther backward, so that their hinder angles begin each to overlap 

 slightly the anterior border of the vertebra next behind. This 

 backward displacement of the upper arches goes on until, in the 

 anterior end of the vertebral column, the bases are placed be- 

 tween two vertebrae and rest equally on both. That is, if we 

 regard each dorsal vertebra as consisting of a pleurocentrum and a 

 hypocentrum united, we may observe that on passing from the tail 

 to the head the pairs of neural bases change from a position of rest- 

 ing each on its own hypocentrum and partly on its pleurocentrum to 

 that of resting partly on- its own hypocentrum and partly on the 

 pleurocentrum of the verteibra next behind. 



As regards the distance of the bases of the successive arches 

 from each other, we find that just behind the head they approach very 

 closely, if they do not come into actual contact. Soon there 

 is a space developed between them, and this increases to near the 

 end of the tail. As regards the relations of the arches to the verte- 

 brae and to neighboring arches, it would almost seem as if Franque 

 had drawn his conclusions wholly from an examination of the ante- 

 rior end of the vertebral column, and Schmidt from the other ex- 

 tremity. 



At the hinder end of the head are two vertebrae which are 

 strongly united to the skull. Their presence is indicated by lines 

 running across this portion of the base of the skull, and by their 

 movable neural arches. The halves of each arch meet above the 

 myelon, but do not unite, nor are they prolonged upward. To the 

 upper ends of each of these arches, or at least the hindermost pair, 

 is articulated a compressed inter-spinous bone (axonost). Sagemehl 

 has already recorded the occurrence of these vertebral bodies, the 

 arches and the axonosts. The lateral halves of the first arch behind 

 the head are prolonged above the neural canal but a short distance. 

 To their upper ends is articulated by a freely movable joint a knife- 

 shaped bone, which must be regarded as homologous with the axo- 

 nosts which support the rays of the dorsal fin. The succeeding 

 arches increase gradually in length. To the second is articulated an 

 axonost similar to, but longer than, the first one. In two specimens 



