Charles R. Bardeen 369 
6. The Muscle Branches of the Plantar Nerves. 
While it is certain that the set of spinal nerves supplying the lateral 
plantar nerve as a group are more distally situated than those supplying 
the medial plantar nerve, the difficulties of tracing the nerves supplied 
to the muscles of the sole back to the sacral plexus make it impossible at 
present to give the spinal nerve supply of these muscles. 
Compared with the other nerves of the leg the plantar nerves seem to 
be unusually constant in their mode of distribution of branches. The 
difficulties of accurate dissection of the nerves of the intrinsic muscles 
of the sole of the foot, however, make it more difficult than in other 
regions to utilize the work of students in getting reliable charts of this 
nerve supply. In general the descriptions given in the various anatomies 
agree pretty well. In the anatomy of Poirier and Charpy the supply 
of the quadratus plante is given as coming from the medial plantar. In 
a large number of dissections which I have followed this branch arose in 
every case from the lateral plantar, usually proximal but sometimes distal 
to the branch to the abductor of the fifth toe. This is the situation 
usually described for it in the text-books. The dissections which I have 
followed also serve to substantiate the statement given in Quain’s 
Anatomy (10th edition) that the lateral plantar nerve only occasionally 
gives a branch to the lateral head of the m. flexor brevis hallucis and to 
substantiate the statement cf Brooks, 87, that in about one in ten in- 
stances the medial as well as the lateral plantar nerves supply both the 
first and second lumbrical muscles. There is, however, considerable 
variation in the way in which the different nerves to the interosseous and 
lumbrical muscles and the transversales pedis are bound for a distance 
in common trunks. 
XI. SUMMARY AND CONCLUSIONS. 
The intrinsic musculature of the inferior extremity in man is differ- 
entiated from the blastema of the limb-bud. No processes from the 
myotomes are sent into the limb from the lumbar or sacral myotomes. 
After the differentiation of the myotomes from the somites the myotomes 
are bounded on the external surface, the sides and ends by a clearly 
marked membrane which is retained until after the lumbo-sacral nerves 
have extended well into the limb-bud. 
Soon after the lumbo-sacral spinal nerves begin to extend into the 
limb-bud tissue differentiation takes place in the blastema of the bud. 
