446 



part of the spinal column, and merely a part of it ossifies to become the 

 basilar part of the coccyx, which Duges was acquainted with, as well as 

 with the two vertebrae of the coccyx above the chorda : the basilar bone 

 is not a body of a vertebra, but coalesces subsequently with the inferior 

 circumference of the coccygeal vertebrae. In these frogs, the coccyx is 

 the only part which arises from both upper and lower vertebral elements ; 

 all the other vertebrae arise in Cultripes and Rana, merely from the upper 

 primitive vertebral elements, which in the course of ossification become 

 divided into arches and central portions. It is only the ossifications of 

 the coccyx which, in these frogs, completely enclose the chorda, since that 

 part is eventually composed of two pairs of vertebrae, and a long basilar 

 piece, whose sutures are retained even in the adult R. paradoxa" (p. 130). 



3. Alytes. With respect to the development of the vertebrae in Alytes 

 obstetricans, Vogt (Entwickelungsgeschichte der Geburtshelferkrote, 1842) 

 states that cartilaginous rings appear in the sheath of the chorda, as 

 rudiments of the centra. Contemporaneously with these the cartilaginous 

 neural arches are developed in the wall of the canal of the medulla; 

 nothing is said as to the mode of ossification. 



4. In both Rana temporaries and Triton, I find that the diaphysis of the 

 vertebra arises as a saddle-like patch, upon, and in immediate contact with, 

 the dorsal surface of the notochord ; the layer of osseous matter is at first 

 exceedingly thin, and gradually extends round the notochord until in most 

 of the frog's vertebrae, and in all of those of the Triton, it forms a complete 

 ring. The osseous deposit in the arches is quite distinct, and has, in the 

 frog, the form of a thin bony sheath investing their cartilaginous basis. 

 The diaphysis of the sacral vertebra remains open below long after the 

 others, and after its neural arch is completely ossified. 



5. The development of the coccyx of the anourous Batrachia has been 

 well described by Duges (7. c. p. 108). The two neural arches originally 

 formed in this region ossify and unite above the spinal cord, and at the same 

 time two osseous centra, which very soon coalesce with them, are formed. 

 These centra are incomplete arcs, open below, where they embrace the 

 notochord. A long cartilaginous plate, however, arises on the ventral 

 surface of the notochord, extending backwards far beyond the level of 

 these posterior coccygeal vertebrae. It ossifies, and eventually becomes 

 anchylosed with the bodies of the coccygeal vertebrae to form the coccyx. 

 Such is the substance of Duges' views, which, as has been seen, have been 

 confirmed in all essential points by Miiller. 



Prof. Owen, however, gives a very different account of the matter. 



" The vertebrae of the tail of the larvae of the Anura are seen distinctly 

 only in the aponeurotic stage. When chondrification occurs, the opera- 

 tion of absorption and coalescence takes place, and two long neurapophyses 

 only are established on each side ; the ossification of these plates extends 

 into the fibrillar sheath of the rest of the coccygeal notochord, and 

 when the perishable parts of the tail of the larva have been absorbed, 

 and the fore- and hind-legs are developed, they constitute by their 

 connation the elongated, osseous coccygeal style, often hollow, of the 

 anourous Batrachia" (Principes d'Osteologie, 1855, p. 186.) 



