447 



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 Duges. I have carefully studied the development of the 

 coccyx in the common frog, and my observations are in entire agreement 

 with those of Duges. Nothing can be more clear than the primitive entire 

 independence of the inferior cartilaginous plate, which by its ossification 

 constitutes the major part of the coccygeal style, from the two neurapo- 

 physes and the rudimentary diaphyses which correspond with them. 



Development of the Spinal Column of Reptilia. 



1. 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 backwards 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 noto- 

 chord, and coalesce with those of the opposite side, so as to form rings 

 which eventually become the bodies of the vertebrae. The upper outer 

 branch extends into the wall of the neural canal, and, eventually uniting 

 with its fellow, forms the neural arch. The lower outer branch extends 

 into the ventral wall and becomes the rib." 



The ring grows both externally and internally, so as to constrict the 

 notochord (which softens and acquires a gnunous consistence), and then 

 becomes converted into bone, so that the notochord is surrounded by a 

 series of bony rings. The notochord takes no part in the formation of the 

 articular intervertebral surface, which is an apophysis and not an epiphy- 

 sis ; the neural arches ossify much later than the centrum, from a single 

 point in the middle of each. The inferior processes are outgrowths of the 

 substance of the vertebra, and in the caudal region are, from the first, 

 double. 



" On each side of the body of the vertebra, where the ribs and the 

 vertebral arches radiate from it, the condensed blastema of which it 

 originally consists, grows out slowly, but considerably, and becomes deve- 

 loped (gradually undergoing chondrification) into a plate, whose largest 

 surfaces are vertical, which increases more in length than in breadth and 

 thickness, and which gradually drives the rib and vertebral arch further 

 away from the axis of the vertebral column. At the end of this period 

 it is almost as thick as the length of the vertebra ; it then appears, when 

 viewed from in front or behind, as a short irregular oblong, one of whose 

 angles passes into the body of the vertebra, and one of whose shorter sides 

 is turned outwards and upwards. From this side passes one crus of the 

 vertebral arch, while from the side which is turned outwards and down- 

 wards, at least in most of the vertebrae, a rib is developed, so that these 

 processes are connected with the originally existing part of the body of 

 the vertebra, only mediately, by the plate in question. 



" The crura of the vertebral arch ossify from their middle towards both 



