OCT. 1895. VERTEBRAL COLUMN OF AMIA HAY 35 



In 1882 Balfour and Parker published their extremely important 

 paper on the structure and development of Lepisosteus (4). They 

 showed in this work that there is surrounding the notochorda cuticular 

 sheath and a very distinct elastica externa. Cartilaginous arches 

 arise both above and below the notochord, their bases coming into 

 contact with the elastica. At a somewhat later stage, there is found 

 to be an almost complete tube of cartilage surrounding the notochord 

 outside of the elastica. This has already been described on another 

 page. At this stage a thin crust of bone envelops the upper and the 

 lower arches and the whole vertebral body. But the bone has not 

 arisen in the elastic layer of the notochord, neither does it extend into 

 this. While its exact place and manner of origin is so far unknown, 

 it apparently does not even arise close to the elastic sheath, but is 

 separated from the latter by the layer of cartilage. Here, so far 

 as we can see and as was believed by Balfour and Parker, the verte 

 brae originate from the union simply of the two sets of arches and 

 their subsequent ossification. 



Klaatsch (41 and 42) holds that the vertebrae of the Teleostomi 

 arise wholly outside of the notochordal sheath. 



Scheele (55) who has investigated Rhodeus among the Cyprinidae 

 and the Trout among the Salmonidae, regards the skeletogenous layer 

 outside of the elastica as giving origin to all the ossified portions of 

 the vertebrae. 



As a result of my investigations I conclude that in Arnia, ossifi- 

 cation of the vertebral centrum does not begin in either the cuticular 

 sheath or in the elastica. On the contrary, it takes its origin wholly 

 in the layer of embryonic connective tissue which lies immediately 

 outside of the elastica. The latter notochordal sheath may be seen 

 in young, just ossifying Amia, and even in adults with a length of 

 i2.5cm., as a bright, highly refractive line immediately between the 

 layer of developing bone and the cuticular sheath. Indeed it is n'ot 

 infrequent that one may distinguish cells resembling bone-cells lying 

 between the elastica and the lamella of growing bone. This is most 

 likely to be observed near the ends of the centra. 



The earliest osseous rudiments of the vertebral body do not form an 

 undivided ring. On the contrary, the bone which is to lay the foun- 

 dation of each centrum starts from a number of distinct points. 

 These are located in the angles between the right and left sides of 

 each half -arch and the adjacent portion of the membrana elastica. 

 There are thus two of these centers of ossification for each half-arch 

 .and two for each of the intercalated cartilages of the middle tail 

 region (Fig. 12). I have thoroughly satisfied myself by the exam- 



