27 
These medullary rootlets represent the spinal accessory nerve 
and constitute its medullary portion. They are described by LESBRE 
as the descending root of the vagus (5). LESBRE and MAIGNON 
have shown that, at any rate in the suidae, the medullary part of the 
spinal accessory nerve is the motor nerve to the viscera, while the 
vagus itself is purely afferent in function (2). 
The spinal portion of the nerve conveys the motor supply to the 
sterno- and brachio-cephalic muscles and in the neck constitutes the 
external branch in the human subject. 
In the camels, the llamas and the giraffes, the spinal portion 
of the spinal accessory is entirely absent, and the above-mentioned 
muscles obtain both their efferent and afferent supply from the 
cervical nerves. 
The clinical importance of the absence in certain animals of the 
external branch or spinal part of the spinal accessory nerve is brought 
out in the paper by M. M. LESBRE and Maicnon. They show that in the 
suidae where the spinal accessory is present, the sterno- and brachio- 
cephalic muscles derive their motor supply from the spinal accessory 
and their sensory supply from the cervical nerves (2). In the camels, 
the llamas and the giraffes, the whole nerve supply—both motor 
and sensory—of the muscles mentioned, is obtained through the 
cervical nerves. Our experiments show that forcible abduction of the 
limb produces stretching and consequent injury of the cervical nerves 
to the brachio-cephalicus, but not of the spinal accessory to that muscle. 
Hence the damage done by an accident of this description to an animal 
possessing a spinal accessory nerve will be less severe and the pro- 
onosis will be better than in an animal in which the entire nerve 
supply of the brachio-cephalicus comes through the cervical nerves. 
This paper is of anature preliminary to the publication of cases 
exhibiting lesions of the nerve-supply to the brachio-cephalicus (9). 
We desire to express our obligation to Professor ELLIOT SMITH 
for his assistance and for allowing us to use some of his unpublished notes 
on the giraffe. We also wish to thank Messrs. JENNISON of Belle 
Vue Zoological Gardens, without whose generous help this paper 
could not have been written. 
