20 
GEORGE E. NICHOLLS. 
At tlie same time I myself (’09) published further evidence 
of the remarkable elasticity of this fibre, its behaviour in the 
case of specimens of Bufo and Petroni j'zon being instanced. 
1 stated definitely that the fibre was not a nerve-tract, and 
that the suggestion put forward by Deiidy as to its function 
was quite in accordance with the facts so far as they were 
then known. 
In the following year, in a joint paper (Dendy and 
Nicliolls ’10), we showed reason for believing that Reissner’s 
fibre, while present almost, if not quite, without exception 
in the vertebrate series from Cyclostoines to Primates, may 
prove to be absent in man. We proposed the name “ sub- 
commissural organ” for the “ependymal groove” with 
which the anterior end of Reissner’s fibre is connected, and 
pointed out that this organ, far from being “inconspicuous in 
mammals” as Sargent asserted, is in reality a very conspicuous 
structure in tlie lower members of this group (mouse, cat). 
It is, however, less conspicuous in the chimpanzee, and, 
while well developed in the fcetal human subject, has become 
reduced to a mere vestige (the “raesocoelic recess”) in the adult 
man. 
Still more recentl}’, Dendy (1910), in an account of the 
pineal organs and adjacent parts of the brain of the tualara, 
has given a short account of Reissner’s fibre and the sub- 
commissural organ in that animal. 
In the present year (’12) I have given a short description 
of the condition of Reissner’s fibre in the sinus terminalis 
of several Elasmobranchs, and described certain experimental 
work carried out by me upon living fish in an attempt to 
ascertain its function. 
(c) General Introductory Account of the Actual 
Relations of Reissner’s fibre and the Sub-com- 
missural Organ. 
As is well known, one of the most constant features — I 
might almost say the most constant feature — in the roof of the 
brain of all vertebrates is that tract of transversely couising 
