EXAMINATION OF SOME SPINAL NERVES 71 
nerves of the right side cut inside the vertebral canal. At 5.30 the final delimitation of the 
border of the Vth cervical completed. 
'The boundary line starts from the mid-dorsal line about 3.5 centims. below the lambda, 
that is, superficial to about the 3rd cervical vertebra ; from that point it sweeps laterally in a 
descending line considerably below the mastoid process. It passes downward behind the sterno- 
mastoid muscle to the clavicle at the junction of the middle and outer thirds of that bone, and it 
then turns horizontally inward along the clavicle to reach the crossed overlap of the skin-fields of 
the nerves of the opposite side of the body, at a distance of about 8 millims. from the mid-ventral 
line.' 
Entire field : — 
Example. M. rhesus, S. At 9.30 a.m. the posterior roots of the Ilird, I Vth, Vlth, 
Vllth, and Vlllth cervical nerves, and of the 1st, Ilnd, and llird thoracic nerves severed. Final 
determination of the isolated field of response at 4 p.m. 
'The field is bounded by a line which starts from near the mid-dorsal line above the 
scapula and on the trapezius muscle. It runs outward in a direction roughly parallel with and 
well above the origin of the deltoid muscle. Continuing this course, it winds round the anterior 
border of the trapezius, curves inwards a little along the hollow between the clavicular portions of 
the trapezius and sterno-mastoid muscles, winds inwards across the front of the clavicular origin of 
the sterno-mastoid, and reaches the mid-ventral line. The posterior edge of the field starts on the 
sternum at the level of the third costal interspace, it then tends laterally, lying about two fingers' 
breadths above the nipple, and attains the lateral edge of the pectoralis muscle after a horizontal 
course. The edge of the pectoralis it follows to the edge of the deltoid, and it then runs along 
the top of the bicipital swelling, rather nearer to the ulnar than to the radial edge of the muscle. 
It enters the forearm over the tendon of the biceps and sweeps down the supinator longus 
prominence, recurving on itself about half-way down the forearm. The field thus includes a 
tongue-shaped area of the forearm, fairly covering the belly of the supinator longus. The boundary 
returns up the arm, passing in front of the outer condyle and up the outer face of the limb along 
the groove between flexors and extensors. It follows the posterior border of deltoid approximately; 
it crosses the spinous process of the scapula near the base of that, and gets to the mid-dorsal line of 
the trunk opposite the spine of the 1st thoracic vertebra ; it slopes suddenly upward near the mid- 
dorsal line, as if it only partially attained to that line.' 
Posterior border : — 
Example. M. rhesus, female. At 9.30 a.m. the posterior roots of the Vlth, Vllth, and 
Vlllth cervical nerves, and of the 1st, Ilnd, and Ilird thoracic nerves severed in the spinal canal. 
Two days later the lower border of the upper field of response finally determined. It agreed with 
the delimitation on evening of first day. It descended the forearm for barely two centims. ; the 
part of the forearm it occupied lay well in front of the external condyle of the crest of supinator 
longus prominence. 
Variation : — • 
A considerable amount was met with in the observations on this field. In one individual 
