314 
fact the outline of the tenth vertebra is well defined (Fig. 4). The 
sides of the neural arch rise up between the ninth and tenth spinal 
nerves, and in larve of the stage figured the ossification extends up 
for about two thirds of the height. The continuous cartilage that forms 
the roof of the ninth, tenth and the potential eleventh and succeeding 
vertebrae is as yet ossified only in the region of the ninth vertebra. 
The undifferentiated eleventh and following vertebre have the form of 
a tube, tapering posteriorly and terminating in a jagged edge. The 
posterior opening is small, and the spinal cord behind this point lies 
unprotected on the dorsal surface of the notochord. The floor of the 
tube is formed by the undifferentiated vertebral bodies, and the imper- 
forate sides and roof by the corresponding neural arches. The uro- 
style is formed, on the disappearance of the notochord, by the union 
of these imperfectly differentiated dorsal structures with the ventral 
or hypochordal splint of bone (wr. Figs. 3 and 4), that is to say, in 
a perfectly normal manner. 
List of authorities referred to. 
1) Avotpu1, H., “Ueber Variationen der Spinalnerven und der Wirbel- 
siule anurer Amphibien”. Teil I. Bufo variabilis. Morph. 
Jahrb., Bd. 19, 1892/93, p. 313—375. One plate. 
2) Avotent, H., Teil II. Pelobates fuscus. Morph. Jahrb., Bd. 22, 
1894/95, p. 449—490. One plate, and four figures in the text. 
3) Avorent, H., Teil III. Bufo cinereus. Morph. Jahrb., Bd. 25, 
1896/97, p. 115—142. One plate. 
4) Bareson, W., Materials for the Study of Variation. London 1894. 
5) Brnuam, W. B., “Notes on an abnormal Vertebral Column of the 
Bullfrog”. Proc. Zool. Soc., London 1894, p. 477—481. One plate. 
6) Bourne, A. G., “On certain Abnormalities in the Common Frog”. 
Quart. Journ. Mier. Se., Vol. 24, London 1884, p. 83—88. One plate. 
7) Bruc#, C., “Ueber die Entwickelung der Wirbelsäule der Rana fusca 
(Pelobates fuscus)”. Wiirzb. naturw. Zeitschr., Bd. 2, Würzburg 
1861, p. 178—198. 
8) Camerano, L., “Nota intorno allo scheletro del Bombinator ig- 
neus”. Atti Accad. Se., Vol. 15, Torino 1879/80, p. 445—450. 
Six figures in the text. 
9) Corr, BE. D., “Sketch of the primary Groups of Batrachia salientia”. 
Natural History Review, N. 8. Vol. 5, London 1865, p. 97—120. 
10) Cops, E. D., “Batrachia of North America’. Bull. U. S. Nat. Mus., 
No. 34, 1889, p. 1—515. Eighty-six plates. 
11) Cuvier, G., Recherches sur les ossemens fossile. T. V, Pt. 2. 
Edit. 4°. Paris, 1824. 
12) Ducks, A., “Recherches sur l’osteologie et la myologie des Batraciens”. 
Mém. Acad. des Sc., T. 6, Paris 1835, p. 1—216. Twenty plates. 
13) Freup, H. H., “Bemerkungen über die Entwickelung der Wirbelsäule 
bei den Amphibien”. Morph. Jahrb., Bd. 22, Leipzig 1894/95, p. 340 
—356. Two plates. 
