445 



ment of the vertebrae of Teleostean fishes, and it is negatived by the 

 observations of Vogt just cited and by my own. 



Development of the Spinal Column of Batrachia. 



1. Anura (Duges, l Recherches sur les Batraciens,' 1835). In the first 

 period the notochord appears to be divided transversely into " rondelles " 

 or vertebrae, but these are not real divisions ; they are appearances pro- 

 duced by the intersections of the muscles which surround the notochord, 

 and of the transverse vascular branches which accompany each pair of 

 nerves when it leaves the medulla. [Duges thus describes the somatomes.] 



In the second period, cartilaginous processes, adherent to the notochord, 

 appear in pairs and enclose the medulla. There are as many of these 

 processes as vertebras will in future exist, and two crests even make their 

 appearance, to form the walls of the coccygeal canal. The apophyses are 

 at first little tubercles j they then bifurcate j one branch becomes the 

 transverse process, the other the neurapophysis with its zygapophyses. 

 In B. fuscus, A. obstetricans, punctatus, and Hyla, where these vertebrae 

 ossify, "two clouds" of ossific matter make their appearance in each 

 vertebra, " as distant from one another as they are from the lateral masses 

 or apophyses," and eventually unite above the notochord so as to form a 

 quadrate ossific centre. This quadrate mass enlarges, but remains con- 

 cave, not only above, but also in front and behind, and especially below, 

 where it forms a semi-canal or groove, in which the notochord is lodged. 

 The groove is gradually filled up, the notochord undergoing a contem- 

 poraneous atrophy, and becoming eventually reduced to a mere ligament. 

 The intervertebral masses are formed altogether independently of the 

 notochord. 



In Rana, on the other hand, the primitive centre of ossification of the 

 body of the vertebra is a ring completely enclosing the chorda j in other 

 respects the development of the spinal column resembles that just 

 described. 



2. Miiller (Vergleichende Anat. d. Myxinoiden, 1835) remarks, " that 

 the formation of the primitive elements of the skull (which are different 

 from the secondary osseous ones) takes place in the higher animals, con- 

 stantly in the same way, is much to be doubted, since variations of the 

 fundamental plan obtain in the vertebral column. In many Batrachia, as 

 Cultripes provincial^, and Rana paradoxa, the bodies of the vertebrae arise 

 only out of the upper primitive vertebral elements. I found, indeed, in 

 the larva of Rana paradoxa, on the under part of the circumference of the 

 chorda dorsalis, a cartilaginous band which was especially well developed 

 posteriorly, in front of the ossification of the coccygeal spine, and was con- 

 tinued, thinner, along the under surface of the chorda, for half the length 

 of the future vertebral column. This cartilaginous band had no fellow, but 

 on the contrary, was thickest in the middle. In the caudal part of the 

 chorda it diminished until it gradually disappeared, so that the inferior 

 arches surrounding the caudal vessels were merely fibrous productions of 

 the external sheath of the chorda. But this inferior cartilaginous band 

 on the chorda of the larva of Rana paradoxa disappears in the greater 



VOL. IX. 2 H 



