550 Stewart Paton 



myotome. Where this latter structure is in a more advanced stage 

 of differentiation tliere the uumber of fibrils forming the bundles 

 is the greatest. This proportionate relaitionship becomes very 

 apparent as we pass caudally; practically to the end of the cord 

 neurofìbrils may be seen, but they diminish greafly in number as 

 the myotome becomes of less structural as well as functional im- 

 portance. 



As would be expected the Sympathetic does not yet exist as a 

 differentiated system, but in certain localities there are conuections 

 betweeu eells that may represeut undiöerentiated tracts. 



In considering- the development of the nervous system and the 

 relation it bears to the primitive movemeuts of the embryo it is 

 important to refer briefly to the conditions present at this period 

 in the myotome. The nuclei in cross sections are relatively small, 

 many are stili round, and only a com})aratively few bave an oblong 

 shape. The boundaries between cells in the greàt majority of in- 

 stances are very indistinctly outlined, and in many places a fusion 

 between the processes has ai)parently taken place giving rise to a 

 definite syncytium corresponding to the descriptiou given by God- 

 LEWSKY, Marceau and others . as characteristic of the early stages 

 in the development of the skeletal muscles in Vertebrates. The 

 place where the first neurofibvils from the ventral root bundles begin 

 to creep along the inner surface of the myotome is a particularly 

 favorable spot to study the syncytium or plasmodium fovmcd by the 

 fusion of the myoblastic cells. At this stage there is no evidence 

 obtained from the study of cross sections of the existence of myo- 

 fibrils. The structure of the myotome may be said to consist as 

 yet merely in cells with variously sliajìed nuclei, and at the difìferent 

 points of fusion of an intervening mass of protoplasm. 



In frontal sections the conditions are more easily studied. The 

 elongated nuclei of the myoblast are oasily recognisable, each con- 

 taining two or more deeply stained nucleoli. "Where the connectious 

 between the myomeres occur, longitudiually arranged faintly stained 

 filaments may be made out that may possibly be primitve myo- 

 fìbrils. 



In contrast to the arrangement of the fibrils noted in studying 

 transverse sections I bave observed that the neurotibrils in the pre- 

 parations cut longitudiually frequently pass into the myotome, but 

 no definite ending can be made out. 



