EXAMINATION OF SOME SPINAL NERVES 87 
agreement between all the clinical observers and the experiments on Macacus ; in the photograph 
of one of my experiments the posterior border of Macaque's skin-field must have agreed point for 
point w^ith Thorburn's figure of that border ; Mackenzie's figure also gives almost exactly the 
same situation for it. In the clinical determination of the posterior border of Vlth cervical the 
limit given it on the hand in Brun's case agrees absolutely with that part of one of my photo- 
graphs of Macacus. But, as stated above, I found frequent sliglit variation of this border in 
Macacus^ and the more usual position of the border in Macacus is one agreeing accurately with 
Williamson's case, and with the right hand in Herter's case. These cases go far to show that 
the agreement in this region between Macacus and Man is very close, extending even to details of 
individual variation. Head's upper patch — a deltoid patch -of the Vlth cervical field is included 
quite identically by Macacus. As to tlie Vllth cervical, Thorburn's fig. 5, which he suggests is 
the Vllth cervical (of course, its posterior border only), closely follows the lines of Macacus^ 
except that it takes in the ulnar edge of ring-finger, which I have never seen quite reached by it 
in Macaque. The Vlllth cervical area of Head in the hand represents with remarkable 
accuracy the central strip of the same field in Macacus^ for it is a strip equidistant from the 
anterior and posterior borders of that field. Also the Vlllth field of Macacus has extensor and 
flexor peaks resembling those of Head's field. Between the fields of the 1st thoracic in Man as 
determined by Head, and that experimentally delimited in Macacus, the correspondence is again 
strikingly close, the latter being, as is inseparable from the difference of the two methods of 
determination, rather the more extensive ; the determinations of the other clinicians for this root 
are not in good agreement with Macacus. In view of the above discussion as to whether the 
Ilnd thoracic nerve contributes to the muscles of the arm in Man as in Macacus, the degree of 
correspondence between the skin-field of the root in the two cases is of special interest. Now, 
Mackenzie's figure (a case of herpetic eruption, v. Barenspung) displays a distribvition of the 
root closely similar to that in Macacus ; and Head's area, determined both by herpetic eruption 
and by reference in visceral disease, gives a still completer correspondence. Other clinical 
observers do not describe the Ilnd thoracic field. The correspondence between this field in 
Man, as described by Head and Mackenzie, is so close as not to indicate that Man's plexus is 
more prefixed than Macaque's. It is true that one occasionally meets with sensory roots and 
motor roots varying independently as regards pre and post fixture ; but that is not the rule. 
I cannot, therefore, help suspecting that our text-books on human anatomy may err in omitting 
the Ilnd thoracic nerve from the human brachial plexus, although I think the above observations 
prove a certain degree of prefixture in the prevailing type of human brachial plexus as compared 
with Macaque's — in this point resembling the Cat's plexus — as compared with Macacus, Rabbit, 
Dog, and Rat. The fact that in Macacus the 1st thoracic does not, as it does in Man, send 
usually a branch to join the Ilnd thoracic, points in the direction of slight prefixture in Man, as 
does the muscular analysis. But Head's and Mackenzie's observations of the area of the Ilnd 
thoracic in Man seem to prove that the amount of his prefixture is after all small. It is certainly 
smaller in this region than in the lumbo-sacral, where, as I have shown in my previous papers, 
that both in regard to muscle and skin the human lies one whole segment in front of {i.e., prefixed 
in comparison with) the Macaque type. 
