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The Nerves and Muscles of the Leg 
IV. OUTGROWTH OF THE NERVES. 
In Embryo CXLIV (length 14 mm.) the main nerve trunks are well 
developed as far as the foot. The relations of the nerves to the spinal 
column, abdominal musculature, skeleton of the limb and the surface 
of the limb are represented in Plate IV, Figs. 1 and 2. The 12th 
thoracic nerve sends a communicating branch to the first lumbar and 
from this latter arise the hypogastric and inguinal branches. 
From the first lumbar nerve a branch is also given off to the lumbar 
plexus. From the 1st and 2d lumbar nerves arise genital and lumbo- 
inguinal branches. ‘The femoral and obturator nerves arise from the 
Ist, 2d, 3d, and 4th lumbar nerves and give off the branches shown in the 
figures. The sciatic nerve, which arises from the 4th and 5th lumbar and 
first three sacral nerves, is composed for the greater part of its course 
of separate peroneal and tibial nerves. The various muscular and cutan- 
eous branches are labeled in the drawing. 
In Embryo XXII, length 20 mm. (Plate V, Figs. 1 and 2), the various 
nerves mentioned are much more highly developed than in Embryo 144. 
This difference of development is especially to be noticed in the feet. The 
figures indicate sufficiently well the relations of the nerves to the skeletal 
apparatus, the skin and the abdominal musculature. 
A noteworthy fact brought out by these figures is that the. cutaneous 
nerves are distributed at first to the anterior, distal and posterior margins 
of the embryonic limb, while the dorsal and ventral regions of the hmb 
are given up to the differentiation of musculature. 
Having thus considered in brief outline the more general features in 
the development of the muscles and nerves of the posterior limb we shall 
take up in turn a more specific study, first, of the development of the 
cutaneous nerves and then of that of the muscles. 
B. DEVELOPMENT AND VARIATION OF THE CUTANEOUS 
NERVES. 
Grosser and Frohlich, 02, have given a good account of the development 
of the cutaneous nerves of the trunk. I have been unable to find any 
specific account of the embryonic development of the cutaneous nerves 
of the limbs, although the work of Sherrington, Head, and others on the 
segmental distribution of these nerves makes it of interest to inquire 
whether or not embryonic conditions can help to explain the phenomena 
these authors have described. In the following section the embryonic 
development and the variations in distribution of specific groups of nerves 
are first described and then the more general facts disclosed by this study 
are briefly reviewed. 
