VERTEBRA 565 



difficult to make out and it is not easy to homologise the parts 

 in all groups. It appears, however, that the general arrangement 



Central 

 nervous 



system . 



Noto chord. 

 Aorta- 



Sclerotome 

 Dermatome \SomLte. 



Myotome 



Gut. 



Nephrotome. 

 Lateral piate. 



coeLom. 



Fig. 441. — A diagrammatic transverse section of part of a mammalian embryo, 



showing the relations of the mesoderm. 



is for the sclerotome of each side to divide into four, from which 

 develop cartilages called arcualia ; these are the interdorsal and 



rn 



f'> 



msv. pr 



ac 



bw. 



Fig. 



442.— Diagram of the organisation of a vertebrate.— From Goodrich. 

 (Young. The Life of Vertebrates, 1950. Clarendon I'ress. Oxford.) 

 ac.. Wall of abdominal coelom ; bd., basidorsal ; hv., basiventral ; b. and feu-., body vN-all ; '^''••^'j"^* ".^^ 

 i., intestine; id., interdorsal; iv., interventral ; m., niyocomma ; ms., '^''^^^""Y lx\x t\tU M 

 dirsal septum ; msv., mediun ventral septum ; nes., neural tube ; ns., notochordal shcith . pr., 

 ventral (pleural) rib ; sp., neural spine ; ts., horizontal septum. 



interventral in front, and the basidorsal and basiventral behind 

 (Fig. 442). The segmental muscle grows between the anterior and 

 posterior pieces, so that the basals of segment ;/ become associated 



