VARIATIONS IN THE POSITION OF THE LIMB-PLEXUSES. 63 
. Lower Limb. 
Cutaneous Distribution. 
Nerves. Spinal Origin. Distribution. 
Ihac branch of twelfth TT. 12. Outer side of buttock. 
thoracic 
Iliac branch of ilio- | L. 1. Outer side of buttock. 
hypogastric 
Tho-inguinal sf le, ile Groin and over Scarpa’s triangle. 
_Preaxial border | Genito-crural . | paleou lee De Front of thigh, upper third. 
_ from trunk to External cutaneous // L. 2. 3. Front and outer side of thigh. 
foot Anterior crural (middle | L. 2. 3. Front and inner side of thigh, 
1 and internal) lower two-thirds. ; 
Obturator . Syl fe bAyeces ene i Inner side of thigh, middle 
third. 
| Anterior crural (inter- | L. 3. 4. Knee and leg, inner side and 
\ nal saphenous) front. 
‘(| Internal saphenous .: | L. 3. 4. Inner side of foot. 
| Anterior tibial. 5 || tba th 4, SS (CI). Interval between first and 
-Dorsmn. second toes. 
Musculo-cutaneous Ibs Bey sh ale Dorsum of foot and toes. 
Root 2 | External saphenous ade (2)e Outer side of foot. 
Internal plantar be 455.82 1 Inner part 
S | _ External plantar 3s ('S2 12: Outer part | of sole. | 
Sole | Posterior tibial (cal- | 8. 1. 2. Heel and back part { | 
| canean) | 
Great toe. i455. Seal 
| 1 = e) 
| Digi Internal and external | L. 4. 5. S. 1. | cleatue foe) Le Riise 
igits . aay eens S19 4 aed os ie oe Seale 
Bae aT ak | Hourth’ 3) 5.8) We: 
Pitth=’ 4, Sel 
| | External saphenous . | S. 1. (2). wees ee of foot and leg, lower 
: | Third. 
postal border | Small sciatic » [hose seas: Back ‘of leg, thigh, and buttock. 
from foot to -| Perforating cutaneous. 8. 2. 3. Buttock (fold of nates, inner | 
peeayes | | : half). 
| “\ Sacro-coccygeal . a ise eh ey Clos Te Anal fold. 
VARIATIONS IN THE POSITION OF THE LIMB-PLEXUSES. 
Two different kinds of variations occur in relation to the limb-nerves. 
(1) Individual variations, in both the extent of origin and in the area of distribution of a 
given nerve, are not uncommon ; these variations are usually concomitant with compensatory 
variations in adjacent nerves, and are due to the fibres of a given spinal nerve taking an 
abnormal course in the trunk of another nerve of distribution and effecting a communication 
with the proper nerve peripherally. In this way the variations in the origin and distribution 
of the intercosto-humeral nerve may be explained ; and, similarly, the ulnar nerve may have 
some of its fibres carried as far as the forearm incorporated with the median and transferred to 
it by a communication between the two nerves in that region. 
(2) Variations in the limb-plexus, in relation to the vertebral column, are the chief cause of 
variations in the constitution of the limb-nerves. These variations affect more or less the whole 
series of nerves in the plexus. 
The brachial plexus is subject only to very slight variation in position and arrangement. 
It may be reinforced at the upper end by a slender trunk from the fourth cervical nerve, and, 
more frequently, by an intra-thoracic communication between the second and first thoracic 
nerves, ‘The presence of one or other of these nerves is an indication of a slight tendency 
towards a cephalic or caudal shifting of the whole plexus in relation to the spinal cord. It is, 
however, never sufficient to cause the exclusion to any extent of the nerves normally implicated. 
The presence of a cervical rib may coincide with little or no change in the relation of the nerves. 
Indeed, the inclusion of the second thoracic nerve in the plexus may be, as already stated, 
merely an individual variation, a change in the path to the limb of the intercosto-humeral 
nerve. Concomitant variations occur among groups of nerves, however, which indicate a certain 
tendency to variation in the position of the whole plexus. At one end, the suprascapular and 
musculo-cutaneous nerves may arise from the fourth and fifth, fifth alone, or fifth and sixth 
cervical nerves. At the other end of the plexus, the musculo-spiral may or may not receive 
a root from the first thoracic nerve, and this addition is rather more likely to occur when the 
second thoracic nerve is implicated in the plexus. 
