630 THE NERVOUS SYSTEM. 
cutaneous nerves otherwise not necessarily concerned in the innervation of the limbs. Herring- 
ham has shown that—(A) Of two spots on the skin, that nearer the preaxial border tends to be 
supplied by the higher nerve. (B) Of two spots in the preaxial area, the lower tends to be supplied by 
the lower nerve ; and, of two spots in the postaxial area, the lower tends to be supplied by the higker 
nerve. In other words, from the root of the limb down the preaxial border to its distal extremity, 
and up the postaxial border to the root of the limb again, there is a definite numerical sequence 
of spinal nerves supplying skin areas through nerves of the limb-plexuses. A similar numerical 
sequence in the arrangement of the nerves is also found extending over the dorsal and ventral 
surfaces of the limbs from preaxial to postaxial border, except in certain situations. 
On the dorsal and ventral surfaces of both upper and lower limbs there is a hiatus, for a 
certain distance, in the numerical sequence of the spinal nerves in their cutaneous distribution, 
explicable on the ground that the central nerves of the plexus, which fail to reach the surface in 
these situations, are replaced by cutaneous branches from neighbouring nerves. This hiatus has 
been named the axial area or line. 
In the upper limb, the dorsal axial area or line extends from the middle line of the back, opposite 
the vertebra prominens, to the insertion of the deltoid. 
The ventral axial area or line extends anteriorly from the middle line of the trunk, at the 
manubrio-sternal joint, across the chest, down the front of the arm and forearm to the wrist. 
In the lower limb, the dorsal axial area or line may be traced from the middle line of the 
back over the posterior superior iliac spine, across the buttock and thigh, to the head of the 
fibula. 
A ventral axial arew or line can also be traced from the root of the penis along the inner side 
of the thigh and knee, and down the back of the leg to the heel. 
These areas or lines represent the meeting-place and overlapping of nerves, which are not in 
numerical sequence ; and it is only at the peripheral parts of the limbs, on the dorsal and ventral 
surfaces, that the nerves appear in numerical sequence from the preaxial to the postaxial border. 
In the case of the upper limb the hiatus is caused, in both surfaces of the limb, by the absence of 
cutaneous branches of the seventh cervical nerve ; in the case of the lower limb the hiatus is due 
to the absence of branches from the fifth lumbar nerve on both surfaces of the limb, and the 
absence of branches from the fourth lumbar nerve, in addition, on the dorsal surface. 
Understanding the significance of these dorsal and ventral axial areas or lines, and at the 
same time bearing in mind the overlapping which occurs in the cutaneous distribution of each 
spinal nerve, the areas of skin supplied through the limb-plexuses can be mapped out with con- 
siderable precision, as indicated in the following tables :— 
A. Upper Limb. 
Cutaneous Distribution. 
Nerves. Spinal Origin. | Distribution. | 
Supraclavicular nerves Gesu | Chest, shoulder, deltoid, and 
a | ey. scapular regions. 
| . | Circumflex . : fo Cx 5G: Deltoid region, outer side of arm. 
_Preaxial border |; Musculo-spiral (upper | C. (5). 6. Outer side and back of arm and 
from neck to +| external) forearm. | 
hand | Museulo-spiral (lower | C. 6. 7. 8. | Outer side and back of elbow 
Y external) | and forearm. 
Musculo-cutaneous . | C. 5. 6. | Outer side of forearm, in front | 
| | and behind. | 
| Radi: NG We er sic ; . 
| Dorswn | sek : les 2 a ae | ot dorsum of hand. 
| J C . . . cnet =i O. ; } 7 = ¥ 
land | f Musculo-cutaneous . | C. 5. 6. Ball of thumb. 
Palm  !| Median ; : anit Gees Outer side)... 
| Ulnar . : : hl Lbs Inner side J OS elo onic 
\| | Thumb, CxGaie 
a First finger, C. 6. 7. 8. 
Ie bac | Median : ? SGH6S 77.4.8) ls Secomdies MOsiieoae lle 
| Digits - = - 4! Ulnar 2 Whole Creer ste Third <) uC. Sain 
| | ee 
| ae Bly %2 
| | Internal cutaneous . | C. 8 T. 1. Inner side of forearm, in front 
| L behind 
| | and behind. 
| Museulo-spiral (inter- | C. 8. 
: al) 
Postaxial border|| , °” . ‘ : 
\hnaetgs : Lesser internal cutane- | T. 1. -| Inner side of arm. 
from hand to 
chest ous aT 
n Intercosto-humeral . | T. 2. | 
| Intereosto-humeral . | T. 2. ‘ 
Third intercostal ep lpaliees: Axillary folds. 
Fourth a t A i oe y 
