110 THOMPSON YATES LABORATORIES REPORT 
In the light of the observations recorded here it is instructive to compare the general 
scheme of root distribvition in the arm with that in the leg. As in the latter,* so in the former, 
the cutaneous spinal fields become distorted from the simple zonal figure obtaining in neck and 
trunk. In the limbs they are displaced, and in the fore-limb in a manner similar to that obtaining 
in the pelvic limb. In each limb the cutaneous spinal segments are dislocated. Instead of each 
being by one of its borders attached to the mid-dorsal line of the body, and by one of its borders 
to the mid-ventral line of the body, the fields are ranged along certain dorsal and ventral lines 
in the limb surface. It is as though into the base of the dorsal surface of the limb the mid-dorsal 
line of the body thrust a spike sidewise, a lateral branch set in a direction almost at right apgles to 
the long axis of the body itself, but corresponding with the long axis of the limb. On the ventral 
surface, similarly, the mid-ventral line of the body thrusts out a lateral branch. These lateral 
branches are what I have termed the mid-dorsal and ?nid-ventral lines of the limb. I have brought 
forward evidence to prove that they are not merely hypothetical, nor even merely theoretical, but 
are existent, and govern skin-markingst to a certain extent. On these secondary dorsal and 
ventral lines the skin segments of the limb are ranged as though on folded pieces of the axial line 
of the trunk itself. 
The Mid-ventral Line of the Upper Limb. 
This line starts from the mid-ventral line of the body, at a point on the sternum opposite 
the lower border of the 3rd costal cartilage. It passes laterally outward and a little upward on 
the pectoral mass, passing about two finger-breadths above the nipple, i.e., somewhat lower 
than midway between nipple and clavicle ; it sweeps out to the upper arm below the anterior edge 
of the deltoid, and runs down the prominence caused by the mass of the flexors of elbow. On 
that prominence it keeps near the inner edge of the biceps ; it enters the forearm upon the tendon 
of the biceps, and may be considered to terminate in the upper third of the forearm, at a point on 
the flexor aspect somewhat nearer the radial than the ulnar border. The fields arising from it in 
front are the IVth, Vth, Vlth, and Vllth cervical, and, in part, the Vlllth cervical. The fields 
arising from it behind are the Ilird, Ilnd, and 1st thoracic, and, in part, the Vlllth cervical. The 
line, when the arm is out straight, runs about at right angles with vertebral column. In nipple line 
it lies just above 3rd costal cartilage, in the mid-lateral line it also lies over 2nd intercostal space. 
The Mid-dorsal Line of the Upper Limb. 
The dorsal line of the upper limb starts from the mid-dorsal line of the trunk, at a point 
opposite the root of the spinous process of the scapula, and just below the level of the head of the 
4th rib. It passes laterally, and reaches the vertebral border of the scapula at the root of the 
spinous process ; thence it slopes downward, crossing the infraspinous fossa just about midway 
between the scapular spina and the inferior angle of the scapula, and meets the posterior border of 
the deltoid eminence, but follows that only so far as to gain the eminence caused by the triceps 
muscle ; along the middle of the crest of this eminence it runs to the elbow, and it enters the 
forearm between the olecranon and the outer condyle close to the latter. It terminates in the 
' Phil. Trans.,' B, vol. 184, 1892, loc. cit. 
t Ibid. 
