116 , THE VERTEBRAL PLATES. 



vertebral plates is formed of a single row of cells, but the 

 inner or splanchnic layer is made up of a central kernel of 

 cells and an inner single layer. This central kernel is the 

 first portion of the vertebral body to undergo any change, 

 and it becomes converted into the main dorso-lateral muscles 

 of the body, which apparently correspond with the muscles 

 derived from the wliole muscle-plate of the Elasmobranchs. 

 From the inner layer of the splanchnic division there are next 

 formed the main internal ventral muscles, rectus abdominis, &c., 

 as well as the chief connective- tissue elements of the parts 

 surrounding the spinal cord. The outer layer of the vertebral 

 plates forms the dermis and sub-cutaneous connective tissue, as 

 well as some of the superficial muscles of the trunk and the 

 muscles of the limbs. 



Dr Gotte appears to think that the vertebral plates in Am- 

 phibians present a perfectly normal development very similar 

 to that of other Vertebrates. The divergences between Am- 

 phibians and other Vertebrates appear, however, to myself, 

 to be very great, and although the very careful account given 

 by Dr Gotte is probably to be relied on, yet some further 

 explanation than he has offered of the development of these 

 parts amongst the Amphibians would seem to be required. 



A primary stage in which the two layers of the vertebral 

 plates are continuous with the somatic and splanchnic layers 

 of a body- wall is equally characteristic of Amphibians, Elas- 

 mobranchs and Mammals. In the subsequent development, 

 however, a great difference between the types becomes appar- 

 ent, for whereas in Elasmobranchs both layers of the vertebral 

 plates combine to form the muscle-plates, out of which the great 

 dorso-lateral muscles are formed, in Amphibians what appear 

 to be the equivalent muscles are derived from a few of the cells 

 (the kernel) of the inner layer of the vertebral plates only. 

 The cells which form the lateral muscles in Amphibians might 

 be thought to correspond in position with the cells which become, 

 in Elasmobranchs, converted into the special early formed band 

 of muscles {m. p'.), rather than, as their development seems 

 to indicate, with the whole Elasmobranch muscle-plates \ 



1 The type of development of the muscle-plates of Amphibians would become 

 identical with that of Elasmobranchs if their first-formed mass of muscle cor- 



