528 Occurrence of a Mesocoelic Recess in the Human Brain. 



adult man, it seems extremely improbable that man possesses any Reissiier's 

 fibre at all. The only primates in which the presence of Eeissner's fibre 

 has yet been demonstrated are Macacus cynomolgiis and M. rhesus (Horsley, 

 1908), and it is perhaps significant that these are both tailed and non- 

 erect forms. 



We may perhaps point out that the suggestion thus put forward as to the 

 possible function of Eeissner's fibre and the sub-commissural organ is not 

 inconsistent with the view previously maintained by one of us (Dendy, 1902), 

 to the effect that in the Ammocoete the latter may serve by ciliary action to 

 promote the circulation of the cerebro-spinal fluid. 



We should like to express our indebtedness to our colleagues Prof. 

 Waterston, Prof. Peter Thompson, and Mr. Frazer, for placing at our disposal 

 some of the material upon which this paper is based, and Mr. E. W. H. Eow 

 for making the photomicrographs used in illustration. 



LITERATURE REFERRED TO. 



Dendy, " On a Pair of Ciliated Grooves in the Brain of the Ammocoete apparently 

 serving to promote the Circulation of the Fluid in the Brain-cavity," ' Roy. 

 Soc. Proc.,' vol. 69. 



Dendy, "On the Parietal Sense-organs and Associated Structures in the New 



Zealand Lamprey {Geotria australis)," 'Quart. Journ. Micr. Sci.,' vol. 51, n.s. 

 Dendy, " The Function of Reissner's Fibre and the Ependymal Groove," ' Nature,' 

 vol. 82, p. 217. 



Gaupp, A. Ecker's und R. Wiedersheim's ' Anatomie des Frosches,' vol. 2. 

 Horsley, " Note on the Existence of Reissner's Fibre in Higher Vertebrates," 

 ' Brain,' vol. 31. 



Nicholls, " Reissner's Fibre in the Frog," 'Nature,' vol. 77, p. 344. 

 NichoUs, " The Function of Reissner's Fibre and the Ependymal Groove," 



'Nature,' vol, 82, pp. 217—8. 

 Sargent, "The Ependymal Grooves in the Roof of the Diencephalon of Verte- 

 brates," 'Science,' vol. 17, p. 487. 

 Sargent, "The Optic Reflex Apparatus of Vertebrates for Short-circuit Trans- 

 mission of Motor Reflexes through Reissner's Fibre ; its Morphology, 

 Ontogeny, Phylogeny, and Function.— The Fish-like Vertebrates," 'Bull. 

 Mus. Conip. Zool., Harvard,' vol. 45. 

 Stieda, " Studien iiber das centrale Nervensystem der Wirbelthiere," ' Zeits. wiss. 

 Zool.,' vol. 20. 



Studnicka, "Der ' Reissner'sche Faden ' aiis dem Centralkanal des Riickenmarkes 

 und sein Verlialten in dem Ventriculus (Sinus) terminalis," 'Sitzungsb. 

 Biilim. Gosell. Wiss. Math, naturw. CI.,' No. 3G. 



DESCRIPTION OF PLATE 14. 



Fio. 1. — Chimpanzee. Photomicrograph of part of a Transverse Section through the 

 P()Hterif)r Kn<l of the I'osterioi' Commissure, showing the Sub-commissural 

 Organ and llio Mesoca'lic Recess, x 34. 



1902. 



1907. 



1909. 



1899. 

 1908. 



1908. 

 1909. 



1903. 



1904. 



1870. 

 1899. 



