Eoss Granville Harrison 199 



grow from the latter into the nuiscle. Self-differentiation of the muscles 

 does not take place. 



2. After the muscles have arisen, their nourishment and further growth 

 during the eml)ryonic period takes place independently of the central 

 nervous system ; they have, so to speak, emancipated themselves from the 

 influence of the latter. 



3. Not until the post-emhryonic life is reached is the dependence again 

 established ; the trophic centers of the s])inal cord and brain then begin 

 action. 



Herbst, oi, analyzes the same data, however, and maintains that it is 

 the sensory nerves including the cells of the spinal ganglia, and not the 

 motor nerves, that are necessary to stimulate the differentiation of the 

 muscular substance in the embryo. Herl^st finds support for this view 

 in Wolff's observations referred to above and also in the fact that in 

 Leonowa's case, as well as in others, the spinal ganglia and sensory nerves 

 alone were present. Herbst and Neumann agree, nevertheless, in holding 

 that the nervous system exerts a formative influence u])on the muscular 

 tissue. The well-known fact that a muscle undergoes atrophic changes 

 after its nerve supply has been cut off, would, at first sight, .uphold this 

 view. The study of normal development likewise affords some evidence 

 which might also be interpreted as lending support to it, though it does 

 not necessarily do so. In the embryos of lower vertebrates, for instance, 

 the connection of the motor spinal nerves with the muscle plates is estab- 

 lished just at the time when the contractile substance begins to be laid 

 down.'' Again, as Nussbaum, 94 (also later publications), has shown in a 

 series of investigations, there is a close parallel between the direction of 

 the intramuscular ramifications of the nerve supplying a muscle and the 

 direction of the growth of that muscle in the embryo, a view which has 

 also been supported by Bardeen, 00. Nusbaum, 02, points out, however, 

 that this correspondence might exist even though there be no dependence 

 on the part of the muscle upon a formative stimulus. 



It is clear from the foregoing that the facts are insufficient to deter- 

 mine even the comparatively simple relations between the nervous system 

 and the developing musculature. The difficulty in interpreting correctly 

 the meaning of the teratological cases, which have been the subject of so 

 much discussion, rests upon our inability to find out the exact nature of 

 the original lesion. The only way to control satisfactorily this factor is 



^ This apparently does not hold for all vertebrates, for, according to Bardeen, 

 00, the musculature of the pig embryo is differentiated to a considerable 

 degree before the nerves establish a connection with it. 



