133 
Recognising the possibility of individual variation, I have di- 
sected more than one specimen of the species, whenever opportunity 
offered and in many cases I managed to obtain several specimens 
of the same genus. In certain instances (e. g. the agoutis) it has 
not been possible to identify the species owing to the animals having 
been in the department for a considerable time. In a few cases 
(e. g. the gibbon) I have been unable to give the species because 
there has been considerable doubt as to what species the animal 
belonged. 
In the technique of the dissection there is one little point worthy 
of note. The intercostal vessel, or one of its branches, lies very close 
to the communication between the first and second dorsal nerves, 
and with careless dissection might conceivably be mistaken for the 
nerve. 
The results of the investigation as tabulated in the appendix 
show that the hinder end of the brachial plexus is exceedingly constant 
throughout the mammalian series. The first dorsal nerve always 
enters the plexus, although this is not definitely stated, but in no 
mammals, with the exception of the cercopithecidae, does the second 
dorsal nerve almost invariably give communication to the plexus. 
In the cercopithecidae the contribution from the second dorsal nerve 
may rarely be absent (see cynocephalus anubis b). 
Another striking point shown by the results is the individual 
variation among the species, in which I have had the opportunity 
of dissecting more than one example. 
The individual variation in the Felidae is the cause of the dis- 
crepancy in the statements given in references (7), (9) and (13). 
Specimen 41 of canis vulpes presented a communication of 
considerable size, while in specimen 2 the communication was al- 
together absent. 
A similar condition is found among the coypus and the wombats. 
The relation of the communication to the sympathetic in certain 
animals was also very suggestive. 
In Synetheres one example exhibited the small nerve as a definite 
part of the sympathetic chain, while in two others it was impossible 
to state definitely by naked eye appearance that the communi- 
cation was actually sympathetic in constitution, although this seemed 
probable. Throughout the paper I have indicated this condition by 
the expression “ uncertain relation 
