622 THE NERVOUS SYSTEM. 
Il. Lower Limb. 
Origin. Nerves. Distribution. 
‘Tho- hypogastric An ue sane Jn) 
Superior gluteal | 
Inferior gluteal Buttock 
Nerve to pyriformis J 
D 1 Small sciatic 
A ee a Re coreeneats 3uttock and thigh, outer side - Dorsal 
Se Ra magia tet ak and front surface 
Genito-crural (crural branch) — Front of thigh 
sees / Front and inner side of thigh, 
Anterior crural ; aye o-p)) 
leg, and foot 
-Peroneal : ; : 5 Front of leg and foot 
Lumbo- !'|———— - = Sle ———— 
sacral < ,llio-hypogastric (hypogastric Abdominal wall (ventral sur- 
Plexus branch) face) 
fei Abdominal wall, thigh, and 
Tho-inguinal : : re} arpa: ug Nea 
: perineum 
Genito-crural (genital branch) Groin 
hic ] ap] 2 ‘ r¢ 1e 
Obtundior Us} eae side) and knee 
; \ \DaACK ) 
\ Ventral . Nerve to obturator internus _ Ventral 
trunks surface 
and superior gemellus 
Nerve to quadratus femoris 
and inferior gemellus 
Nerve to hamstrings | 
Small sciatic : 3ack of thigh and perineum 
Tibial { Back of knee, leg, and sole of 
: : \ foot 
Buttock and back of thigh 
In the regions of the limbs no anterior cutaneous branches, derived from the limb nerves, 
supply the trunk. The whole of the nerve is carried into the limb and is absorbed in its 
innervation, and the dorsal and ventral trunks forming the limb-plexuses are to be looked upon 
as homologous with the lateral and anterior trunks “of an intercostal nerve. Two series of 
anomalies in relation to the formation and distribution of the nerves to the limbs must, however, 
be considered, because it has been suggested (Goodsir) that the nerves of the limbs are serially 
homologous with not the whole, but with only the lateral branches of the anterior primary 
divisions of the intercostal nerves. 
(1) Nerves in connexion with the primitive borders of the Limbs.—At the preaxial 
border of the upper limb, at its root, the fourth cervical nerve, which supplies the anterior and 
lateral surfaces of the neck, is also distributed through the supraclavicular nerves to the skin of 
both ventral and dorsal surfaces of the limb. The nerves and surfaces are here not merely 
homologous, but in actual continuity. 
At the preaxial border of the lower limb, similarly, the first lumbar nerve, by means of the 
ilio-hypogastrie and ilio-inguinal branches, supplies on the one hand the buttock, in series with 
the lateral branches of the lower thoracic nerves, and, on the other hand, the low er part of the 
abdominal wall and the adjacent inner side of the thigh, im series with the anterior terminal 
branches of the lower thoracic nerves. 
At the postaxial border of the upper limb the first and second thoracic nerves are concerned 
in supplying trunk segments as well as parts of the limb. The first thoracic nerve, besides 
supplying the limb through the inner cord of the plexus, also innervates at least the muscles of 
the first intercostal space ; the second thoracic nerve is concerned in the innervation of the limb, 
principally by means of its lateral branch only, which, as the intercosto-humeral nerve, supplies 
the skin along the postaxial border of the limb ‘and on its dorsal side. At the postaxial border of - 
the lower limb, in the same way, the third and fourth sacral nerves, partially implicated in the 
innervation of the limb (through the tibial, small sciatic, perforating cutaneous nerve, and 
perineal branch of the fourth sacral nerve), are also engaged in supplying the trunk (perineum) 
through the pudic nerve. These peculiarities of arrangement of the nerves at the borders of the 
limbs 1 may be explained on the supposition that the segment corresponding to the nerve named 
is only partially concerned in limb formation, and is, at the same time, implicated to a greater 
or less extent in the formation of structures belonging to the trunk. 
(2) The origin and distribution of the nerves at the postaxial border of the limbs present 
a special difficulty. In the composition respectively of the brachial and lumbo-sacral plexuses, 
the first thoracic and third sacral nerves do not as a rule divide into ventral and dorsal trunks, 
but contribute only to the formation of the ventral series of nerves. A solution of this difficulty 
may be found in the examination of the areas of distribution of the nerves derived from the 
first thoracic and third sacral nerves. In the case of the brachial plexus (the inner cord of which 
