EXAMINATION OF SOME SPINAL NERVES 93 
given by the sensory roots of these nerves to the muscular parts or the limb is taken into account, 
a ray of muscular and other tissue is found to extend between the sensory skin-cap supplied by the 
nerves of the apex of the limb only and the median plane of the body. The proximal portion of 
the sensory ray exists, but buried beneath the surface ; this proximal part is therefore now^here 
cutaneous, but is mainly muscular ; the sensory ray in the muscular and non-cutaneous tissue 
stretches from its base in the muscles and ligaments of the vertebral column to an apex in tlie 
muscles and ligaments, etc., of the foot. 
By the experiments cited this has been shown for the lower limb ; it is also true tor the 
upper limb and the Vllth and Vlllth cervical and 1st thoracic nerves. The dorsal primary 
divisions of these nerves, like those of the Vth, Vlth, and Vllth post-thoracic, do not possess 
cutaneous branches, thus differing from the primary dorsal divisions of all the other cervical and 
thoracic nerves. 
Experiment. M. rhesus. The Vth, Vllth, Vlllth cervical, and the 1st, Ilnd, and Ilird thoracic 
nerves cut in the vertebral canal proximal to the root ganglia. Time allowed for degeneration 28 days. 
The primary dorsal divisions of the 1st thoracic and Vlllth and Vllth cervical nerves on excitation evoked 
no muscular contraction, but when teased and when examined in serial sections, a number ot sound 
myelinate nerve-fibres were found in them ; these must have arisen in the spinal ganglia. The muscular 
branches of the ulnar nerve contained a certain number of sound myelinate fibres (not so many as in 
instance quoted from the lower limb) ; so also the inner head of the median nerve, but neither of these 
trunks on faradic excitation evoked muscular contractions. 
It has been shown above that the distribution of the sensory root-fibres in the last two 
cervical, and in the highest thoracic nerve, is, as regards skin, confined to the hand, forearm, and 
lowest part of the upper arm, nowhere approaching to the median line of the body. If we 
include the sensory fibres distributed to the deep parts, the distribution of these nerves does, 
however, come right up to the median plane, including the muscles and ligaments of the vertebral 
column. Thus in the upper limb, as in the lower, the sensory ray, when its nerves are examined 
by experimental degeneration, is proved to extend from the apex of the limb to the median 
plane of the body, in fact, to be a complete ray. The proximal part of the ray, however, just as 
in the pelvic limb, nowhere reaches the body surface, but lies beneath the surface, and is composed 
of muscles and deep tissues. If judged by skin alone it is wanting. 
It becomes clear that absence of cutaneous branches from the dorsal primary divisions of 
the Vllth, Vlllth cer\'ical, and 1st thoracic, and from the Vth, Vlth and Vllth post-thoracic 
nerves, proves to be simply a natural concomitant of their segmental position in the spinal series, 
and is a criterion indicating that they lie at the very centre of the limb regions, respectively 
brachial and pelvic. 
IV. The spinal roots which are the source of the aflfercnt nerve-fibres of the hamstring 
muiclei can be determined by use of vaso-motor and of respiratory reflexes. The individual 
dorsal (posterior) roots through which the afferent nerve-fibres from a muscle pass, can be found 
by noting which are the roots whose section lessens or abolishes the reflex. In the case of the 
hamstring muscles or the Cat, I find these roots, subject to individual variation, are the Vllth, 
Vlllth and Vlth post-thoracic ; now the Vllth, Vlllth and Vlth nerves are exactly those the 
