ON THE THEORY OF THE VERTEBRATE SKULL 597 



centra. Contemporaneously with these the cartilaginous neural arches are de- 

 veloped in the wall of the canal of the medulla ; nothing is said as to the mode of 

 ■ossification. 



4. In both Rima temporaria 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 exceed- 

 ingly 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 Dugfes (/. 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 in- 

 complete arcs, open below, where they embrace the notochord. A long carti- 

 laginous 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 vertebra to 

 form the coccyx. Such is the substance of Dugfes' 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 larvse of the Anura are seen distinctly only 

 in the aponeurotic stage. When chondrification occurs, the operation of absorption 

 and coalescence takes place, and two long neurapophyses only are estabhshed 

 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.) 



Prof Owen does not state on what anourous batrachian his observations were 

 made, nor does he notice the wide discrepancy between his views and those of 

 Dugfes. I have carefully studied the development of the coccyx in the common 

 frog, and my observations are in entire agreement with those of Dug^s. Nothing 

 can be more clear than the primitive entire independence of the inferior carti- 

 laginous plate, which by its ossification constitutes the major part of the coccygeal 

 style, from the two neurapophyses and the rudimentary diaphyses which correspond 

 with them. 



Development of the Spinal Column of Reptilia. 



I. Ophidia (Rathke, ' Entw. der Natter,' 1839).— "Quadrate plates of a more 

 solid substance than the rest of the blastema appear on each side of the notochord, 

 in the middle of the body, where they are at first largest, diminishing in size back- 

 wards and forwards. At first they extend neither into the dorsal nor into the 

 ventral plates of the embryo. 



"These plates increase in length, and those of each pair grow towards one 

 another above and below. Each plate grows out into two branches above and 

 below. The inner branches lie in close contact with the notochord, and coalesce 

 with those of the opposite side, so as to form rings which eventually become the 

 bodies of the vertebras. The upper outer branch extends into the wall of the 



