EXAMINATION OF SOME SPINAL NERVES 85 
present in the Macaque, I have never met with this forearm branch in Cercocelms nor in 
Cynocephalus. These latter forms do possess, however, the somewliat similar communication 
between external saphenous nerve and external plantar at the heel deep to the tendo Achillis, 
which I described and figured in my former paper in Macacm* The contribution from ulnar to 
median contains cutaneous sensory fibres as well as motor efferent (see p. 102, fig. 11, p. 103, 
below). The communication between ulnar and median is normal in most Mammals.t In Man 
it occurs in 20 to 25 per cent, of individuals,^ a fact which lends more interest to the physiological 
analysis of the communication as it exists in Macacm. 
It will be noted that although the Ilnd thoracic nerve contributes to the innervation of the 
muscles of the hand and lower forearm, it does not contribute to the sensory innervation of any 
part of the skin of the hand, nor even to that of the lower part of the forearm. Also, although it 
supplies the muscles of the second intercostal space, the skin overlying the second intercostal space 
is not innervated by it. I have already pointed this out as a striking illustration of the want 
of real basis for the so-called ' law ' (Van der Kolk, Hilton), which states that muscles and 
their overlying integument are supplied by the same segmental nerves. The skin over the first 
and second intercostal spaces is in great part innervated from segments five and six, segments 
further headward than the source of innervation of the underlying muscles, e.g.^ first intercostal 
space : muscles, 1st thoracic, skin, IVth cervical. 
In concluding this section a few words are desirable regarding the comparison between the 
segmental anatomy of Man and of Macacm in this region. Beyond question the similarity 
between the two is almost minutely exact. The most salient point of difference appears in the 
motor distribution of the Ilnd thoracic root, which is not generally considered to contribute to the 
brachial plexus in Man. Its contribution is of almost universal occurrence in the animals used in 
the Laboratory. I have tested the point by dissection and stimulation in the Dog, Cat,§ Horse, 
Rabbit, and Rat, as well as in Monkeys, and find it among the types examined of inconstant pre- 
sence in the Cat and Dog only : it is more frequently absent in Cat than in Dog, and sometimes 
on one side only. That a communicating branch often passes in Man from Ilnd thoracic to 1st 
thoracic has been seen by Cunningham, who found it in 70 per cent, of the individuals examined. 
If the Ilnd thoracic does not really contribute to the human brachial plexus, the plexus of Man is 
prefixed as compared with that of the other types. Now in the Macaque the rectus capitis anticus 
major is supplied not from the 1st cervical root as in Man. The Scaleni^ all three, are present in 
Macaque as in Man, but they receive a more posterior root supply than in Man, the upper two 
thoracic roots contributing to their innervation, whereas the Ilnd and IlIrd cervical roots do not 
contribute to them in Macacus, though they do so in Man. In the Macaque I have in one 
individual found the Ilird cervical motor root innervating the diaphragm (ventral part), but in 
* 'Journal of Physiology,' vol. 13, p. 643, Plate 21, fig. 7. f Bardeleben. 
J Quain's 'Anatomy,' vol. iii, part 2, p. 302. Thane, 1895. 
§ My results on this point were demonstrated to the Physiological Society, Feb. 13th, 1892. At that date Dr. Langley had 
already (Jan. 20lh) sent in a paper to the Royal Society ('Origin of the Cervical ami Upper Thoracic Fibres of the Sympathetic* 
Read Feb. 18th. 'Phil. Trans.,' B, 1892) in which, as regards the Cat and Rabbit, results similar to my own had been arrived 
at. loth July, 1897, C.S.S. 
