34 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. i. 



Von Baer (2 p. 36), basing his conclusions on his studies especially 

 of the Cyprinidae, thought that no part of the vertebra is derived from 

 the notochord or its sheaths. For him the vertebra was formed 

 through the simple union of the bone arising from the upper and the 

 lower arches and extending around the notochord so as to produce 

 a ring. 



From the study of Blennius viviparus Rathke (51) concluded that 

 each vertebral centrum arises from ossifications which are located in 

 the bases of the upper and the lower arches, which four points by 

 their union form a ring. Later Rathke (52) appears to have accepted 

 J. M tiller's view that the vertebral ring is distinct in its origin from 

 the arches. 



Johann Miiller at first (49, Osteology, pp. 83 and 143) held the 

 opinion that ossification of the vertebral column begins outside of the 

 notochordal sheaths, and that the vertebra is composed wholly of the 

 arches and the ossifications arising in them. Later, from studies on 

 the Elasmobranchs, he concluded (49, Neurology, p. 69) that in the 

 case even of the osseous fishes, the notochordal sheath ossifies, and 

 that an undivided ring is formed independently of the arches. The 

 vertebra then consists of the upper and the lower arches and the cen- 

 tral ring. 



August Miiller's views are essentially those of Johann Miiller (48, 

 p. 260.) 



Gegenbaur has expressed his conclusions on the origin of the ver- 

 tebral body in his paper on Lepisosteus (28.) He believes that the 

 centrum arises outside of the elastica externa, and that it proceeds 

 from the arches themselves. 



Theophil Lotz (45) made investigations on Salmo salar. For him 

 the vertebral centrum arises outside of the elastica, its earliest ap- 

 pearance being at the points of contact of the lower arches with the 

 notochordal sheaths. It then grows upward on each side of the no- 

 tochord, and its extremities at length pass under the bases of the 

 upper arches and meet above the notochord to form a complete ring. 



Oscar Cartier (13) agrees with Lotz, except that he finds that the 

 ossification which produces the ring arises in the elastica. The latter 

 disappears as the ring is developed. 



Goette (32 and 33) contends that ossification begins in what is 

 usually called the elastic sheath. He denies the elastic nature of 

 this sheath, and holds that it is cellular in structure. The centrum 

 is developed from below upward, as taught by Lotz and Cartier. 



Balfour, in 1881, in his Comparative Embryology appears to 

 accept in general the views of Goette. 



