454 



regarded as a continuatiou and amplification of my earlier work on 

 the subject. 



The material upon which my results are based consisted partly 

 of a number of adult living Tuataras presented to me by the New 

 Zealand Government, the cost of transmission of which to England 

 was defrayed by a grant from the Government Grant Committee, and 

 partly of specimens (chiefly embryos) preserved by myself while in 

 New Zealand. I defer the expression of my thanks to the numerous 

 friends who have helped me in the work until the publication of the 

 complete memoir. 



As I have already pointed out in my work on the intracranial 

 vascular system i), there is in Sphenodon a very extensive subdural 

 cavity between the brain and the cranial wall, and advantage was 

 taken of this fact to fix the delicate organs of the pineal complex in 

 situ by the injection into the cranial cavity of acetic bichromate of 

 potash. After fixation the pineal eye itself, with the parietal plug, 

 can bo dissected clean out of the parietal foramen, and the necessity 

 of decalcification before section cutting thus avoided. 



The "pineal complex" is formed chiefly by the dorsal sac, the 

 paraphysis, and the pineal sac ("epiphysis" or right, pineal organ), 

 united in a common pial investment and forming a bilaterally flattened, 

 funnel-shaped structure attached above to the cranial roof by the 

 dura mater and below to the optic thalami and habenular ganglia. 



Across the subdural space numerous fine threads of connective 

 tissue extend from the surface of the brain to the dura mater, and 

 these are concentrated to form imperfectly developed vertical sup- 

 porting membranes for the pineal complex, one placed transversely on 

 either side of the dorsal sac and one lying in the sagittal plane behind 

 the pineal sac. The very large subdural space arises late in devel- 

 opment, which perhaps indicates that the relatively small size of the 

 brain is a csenogenetic character due to arrested growth. 



The fundamental relations of the different parts of the fore-brain 

 and its derivates in Sphenodon are already to a large extent familiar 

 to us, but the following points may be noticed: 



Gisi has described the lateral choroid plexuses (plexus hemi- 

 sphserium) as arising from a transverse fold behind the paraphysial 

 opening, while Elliot Smith has described them as arising from a 

 transverse fold in front of the paraphysial opening. The explanation 

 of this discrepancy is that while they really arise one on either side 



1) Phil. Trans., 1909. 



