OCT. 1895. VERTEBRAL COLUMN OF AMIA HAY 17 



are apparently somewhat more independent of the haemal arches, but 

 there seems to be no reason why this condition should not be the re- 

 sult of specialization. 



A microscopical examination of the caudal region of a specimen 

 about 1 2 smm. in length, has given me results which may be of some 

 value. 



The last but one of the " complete" vertebrae is in all respects 

 similar to the vertebrae preceding it. Both arches, the upper and the 

 lower, sit upon cartilaginous bases, and these latter penetrate close 

 to the notochord. The next vertebra, like the corresponding verte- 

 bra in each of the two specimens microscopically examined, lacks the 

 neural spine, while also the lateral halves of the neural arch appear 

 not to meet over the spinal canal. The cartilages on which the neu- 

 ral arch is based reach nearly to the center of the vertebra, so that 

 on the upper side the notochord is constricted, just as in the case of 

 the more anterior vertebrae. The haemal arch, on the contrary, has 

 no such broad cartilaginous bases, although its proximal end contains a 

 nodule of cartilage. The lower arms of the cross seen in cross-sections 

 of the more anterior vertebras are here wanting, and the lower side 

 of the notochord is extremely little constricted. The ossified hypural 

 spine is consolidated with a thin shell of bone which forms the lower 

 side of the vertebral centrum. The appearance presented suggests 

 that the base of the haemal spine has originated at a relatively late 

 period in the development of the individual, so that it has not stood 

 in the way of the growth of the notochord. 



Giving our attention to the five vertebrae which follow the one 

 just described, we find that each possesses the upper arms of the car- 

 tilaginous cross and that upon the ends of these arms, rest the edges 

 of the strip of cartilage which roofs over this part of the spinal canal ; 

 just as the neural arches of the more anterior vertebrae rest on the 

 upper ends of the cartilaginous crosses of their respective vertebrae. 

 Moreover, that part of this roofing cartilage which overlies the first two 

 of these last five vertebrae is almost wholly segmented off from that 

 behind it by an incision which begins in the lower border and runs 

 upward. This, taken in connection with the spineless condition of 

 the vertebra just preceding, presents a gradual transition between 

 the normal neural arches and those which have become concrescent ; 

 so that it is quite certain that this anterior portion of the prolonged 

 cartilage is made up alone of the neural arches. It is also to be ob- 

 served here that the upper side of the notochord has suffered con- 

 striction at the points touched by the lower ends of the intravertebral 

 cartilages. 



