456 PKOr. G. ELLIOT SMITH ON THE MOEPHOLOGT OF THE 



Zealand, where it was impossible to consult all the recent literature relating to this 

 region of the brain, and hence he used the term " commissura fornicis," which was the 

 original name applied to this tract of fibres by Eabl-Riickhard. I might add, in passing, 

 that this original and now discarded term is unquestionably the least objectionable of the 

 names hitherto ajiplied to this conmiissure. 



In addition to devoting himself to the study of the early developmental history of the 

 Tuatara, Professor Deudy also collected a valuable series of embiyos, which were sent 

 to Professor Howes in order that the histogenesis of the skeleton might be fully 

 investigated. After a number of beautiful series of coronal and sagittal sections of 

 embryos of various ages had been made by Mr. Swinnerton for this work *, Professor 

 Howes kindly suggested to Professor Dendy that I should study the developmental 

 history of the nervous system in the sjiecimens iu whicli he was investigating the skeletal 

 structures. Professor Dendy kindly gave his consent to this suggestion, and in addition 

 offered to obtain specimens of properly j)reserved adult brains. During the year 1899 I 

 devoted most of my vacations to the examination of this valuable material in Professor 

 HoAves's laboratory at the Royal College of Science, where these notes were written. As 

 I left England shortly afterward, I have had no chance of seeing the material again, and 

 as there seems little prospect of doing so in the immediate future, I am publishing in this 

 incomplete form the most interesting observations of which I had made a record. In 

 order to enhance the value of this, which being so imperfect is in itself slight, I have 

 introduced into the account a series of comparative notes, which 1 believe will shed some 

 light on one of the darkest and least-understood corners of the brain, and help towards 

 systematizing our knowledge for the future. 



The roof of the forebrain of Sphenodon presents an exceedingly irregular form (tig. 1). 

 It consists of a thin layer of epithelium which, attached in front to the dorsal extremity 

 of the lamina terminalis, ends posteriorly at the situation of the habenular (" superior '") 

 commissure by becoming continiious with the thicker epithelium of the parietal stalk. 

 Its irregular course between these two points is represented on a greatly-enlarged scale 

 in figvire 2. From the upper end of the lamina terminalis (a) the epithelial layer bends 

 downward in the third ventricle and, after being thrown into many folds, ascends again 

 and becomes continuous with a long, narrow, irregular evagination of the roof, which is 

 commonly known as the paraphijsls. The irregular fold (/3), which is invaginated into 

 the ventricle between the lamina terminalis and the paraphysis, is pi'olonged laterally on 

 each side into a complicated fold which extends through the foramen of Monro into the 

 lateral ventricle. As these lateral processes are kno"mi as the choroid plexuses, the fold 

 /3 may be distinguished as the lamina chorioklea (generally spelt "choroidea" in English 

 works). The paraphysis is separated from a much longer and broader outgrowth of the 

 roof (y) by a simple transverse lamina, which is commonly called the " velum." The 

 irregular fold y is known as the " dorsal sac." 



The varied nomenclature which is applied to these structures has been discussed in 



* Vuh G. B. Howe.s and H. H. iSwiniiorton, '■ On the Dovelojjinent of the Skeleton ot the Tuatara," Trans. Zool. 

 >Soc., vol. svi. (1001) part 1, for an account of the material. 



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