SoRENSEN, Neurological Laboratory Notes. 53 



words, resembles the so-called epiphysial vesicle of Phrynosoma. 



In the turtle the entire outgrowth from the roof of the 

 Diencephalon resembles in size and the relative position of its 

 parts the epiphysial structures of the horned toad already de- 

 scribed. 



The epiphysis arising immediately behind the supra-com- 

 missure and grows forward by a somewhat narrow stalk, which 

 soon expands to form the vesicle of the epiphysis. This vesicle 

 is somewhat irregular in that several lobes project from the main 

 vesicle. The whole structure is highly vascular, the walls being 

 permeated with numerous blood vessels. 



The epiphysis rests on the slender lamina of the plexus, 

 which runs forward to the cephalic extremity of the epiphysial 

 vesicle and there becomes intricately plicated. The infolding of 

 the plexus at this point forms between this plicated structure 

 and the cephalic origin of the plexus, another structure which is 

 also found, formed in apparently the same way, in snakes, and 

 which I have called for convenience the dorsal sac. This sac 

 runs dorsal toward the cephalic end of the epiphysial vesicle. 



Just in front of the cephalic end of the plexus is a large 

 blood sinnus which runs the whole length of the dorsal sac and 

 joins a blood vessel above. 



The whole structure, including the epiphysial vesicle, plexus, 

 and dorsal sac is extremely vascular. 



EXPLANATION OF PLATE XL 



BAWDEN. 



Fig. I. Part of a median-longitudinal section of the head of a duck-embryo 

 at six-days illustrating the relations between the chorda and pharyngeal sac. 

 The relation of the commissures of the diencephalic roof to the epiphysis may 

 also be seen. 



Fig. 2 The pharyngeal sac and hypophysis from the preceding section. 



Fig. J. The same region from a much older embryo. 



Fig. 4. A similar section from a chick of four or five days. 



Fig. J. Median-longitudinal section through the head of a duck embryo 

 somewhat older than that figured in Fig. 2. 



