ON THE FATE OF THE MUSCLE-PLATE. 109 



On the Pate of the Muscle- Plate, and the De- 

 velopment of the Spinal Nerves and Limb 

 Plexuses in Birds and Mammals. 



By 



A. itl. Paterson, M.D., 



Senior Demonstrator of Anatomy, and Lecturer in Dental Anatomy and 

 Physiology, in the Owens College, Manchester. 



With Plates VII and VUI. 



The late Professor Balfour 1 showed that the spinal nerves in 

 Elasmobranchs spring entirely from epiblastic origins, and the 

 same has been proved conclusively regarding the roots at least 

 of the spinal nerves in birds and mammals, by the researches 

 of Milnes Marshall, 2 His, 3 and others. The most complete 

 account of the early stages in the development of the nerves 

 in higher Vertebrates is that of Marshall. 2 He has traced the 

 roots of the nerves from their origin from the spinal cord to 

 the point when they unite together to form the mixed nerve. 

 Prom that point onwards there is uncertainty. Though it is 

 considered highly probable that the further growth of the 

 nerves consists of an extension towards the periphery of the 

 original epiblastic elements, still it has not been proved that 

 this is so. It has not hitherto been shown that the nerve- 

 trunks, after the junction of the two roots, are not formed from 

 the cells of the mesoblast. 



1 c Monograph on the Development of Elasmobranch Fishes,' London, 1878. 



2 'Journal of Anatomy and Physiology,' vol. xi, p. 491. 



3 " Ueber d. Anfange d. Peripberischen Nerven Systems," ' Archiv f. Anat. 

 u. Pliys.,' 1879. 



