OCT. 1895. VERTEBRAL COLUMN OF AMIA HAY 19 



the underside of this tube is a furrow, at first shallow, but growing 

 deeper towards the hinder end. In this furrow runs the notochord. 

 Near the tip of the cartilage the edges of the furrow meet and co- 

 alesce below the notochord. Kolliker's figures show a relatively 

 thick wall of cartilage everywhere between the spinal cord and the 

 notochord. In my sections there is, on the contrary, from the last 

 ossified centrum to the tip of the notochord, no cartilage between 

 the latter and the spinal cord. The narrow space between them is 

 occupied by loose connective tissue and blood-vessels. The lower 

 borders of the cartilage incline inward between the two structures, 

 but do not meet. The condition described by Kolliker is probably 

 .attained at a more advanced age. Farther back, at a point some dis- 

 tance behind the distal ends of the hypurals, the cartilage gradu- 

 ally spreads downward over the sides of the notochord, and finally 

 completely encloses it. Under these circumstances it appears to me 

 probable that this whole strip of cartilage has resulted from the 

 downward extension of coalesced neural arches, and none of it from 

 the lower arches. It is also interesting to observe that there are in 

 this portion of the terminal cartilage seven shallow nicks along its 

 lower border. These suggest a partial separation into distinct seg- 

 ments. 



The notochord in this region has a thick cuticular sheath, outside 

 of which is to be distinctly seen the elastica externa. In my sections 

 -of the hinder tail region of the specimen 125111111. long, the noto- 

 chordal sheath is far from having a structureless appearance. Espec- 

 ially along the portion where the incomplete vertebrae are developed, 

 but also further backward, the sheath is traversed from elastica to 

 notochord by lines, or fibers, of some substance which stains deeply 

 with carmine. Where the notochord is constricted by the upper por- 

 tion of the incomplete vertebrae, these fibres appear to start from the 

 lower surface of the elastica. Here they are so close-set as to resem- 

 ble the hairs of a brush, but as they approach the inner surface of the 

 sheath they become finer and less numerous. 



In this same region the inner cuticular sheath has undergone 

 another modification, to which I will call attention. Where the last six 

 vertebrae of the upturned portion of the tail have constricted the 

 notochord, especially on the upper side, we find that the outer half, 

 or somewhat less, of the cuticular sheath stains deeply. One is 

 reminded of the modification suffered by the sheath of the notochord 

 of Lepisosteus, as described by Balf our and Parker (4, vol. i, 781; 

 vol. iv., pi. 41 (Fig. 69). InAmia, however, the pulley-like band so 

 modified does not extend far forward and backward beyond the 



