John Warren lye 
the paraphysis. The velum and the greater part of the post-velar arch 
have been absorbed in the formation of the diencephalic plexus. A 
portion of this arch, however, persists and forms that part of the roof 
of the diencephalon between the diencephalic plexus and the supra. com- 
missure. The epiphysal arch has formed the epiphysis. 
The paraphysis is a structure common to all vertebrates either in the 
adult or embryonic condition (Selenka, 34, Francotte, 11), but previous 
observations on mammals leave much to be desired. It always arises from 
the telencephalon cephalad to the velum transversum, and its opening 
is placed between and dorsad to the foramina of Munro as emphasized 
by Dexter (5). 
In the cyclostomes, Ammocoetes (Kupffer, 24), and Petromyzon 
(Burckhardt, 3), the paraphysis appears as a small sac-like diverticulum 
lying ventrad and close to the enlarged distal end of the epiphysis. In 
elasmobranchs, Minot (28) and Locy (27) found that the paraphysis 
in Acanthias appears at quite a late stage as a small outgrowth from 
the paraphysal arch and, owing to the small size of the post-velar arch 
and the compression of the velum, it comes to lie immediately cephalad to 
the epiphysis. In ganoids, Kupffer found in Accipenser that the para- 
physis appears first as a small outgrowth which later becomes a somewhat 
sacculated vesicle (23, Fig. 19). Hill (18) and Eycleshymer and Davis 
(9) studied the paraphysis in Amia. Here it begins as a simple vesicle, 
which increases rapidly in size and gives off diverticuli from its central 
cavity. In teleosts (Burckhardt, 3) the paraphysis appears late and 
remains in a rudimentary condition. In the dipnoi, Burckhardt (3) de- 
scribes the paraphysis in Protopterus as a wide outgrowth giving off small 
diverticul. ) 
In amphibia the organ becomes highly differentiated and its appear- 
ance in the adult brain is very striking. It appears as an elongated body 
lying above and between the hemispheres, and extending cephalad for 
a varying distance in various forms, Fig. 23. Osborn (31, Pl. 4) shows 
a view of the brains of Siredon, Necturus, Proteus, and Siren. The 
paraphysis has the same general form in each of these, but it is somewhat 
larger in Necturus. The paraphysis of Triton and Ichthyophis (Burck- 
hardt, 4) has the same characteristics. In the latter the paraphysis ap- 
pears in sagittal section as a hammer-shaped organ extending forward 
above the hemispheres. (4, Fig. 1). In Rana the paraphysis has the 
same position as in Necturus, but is smaller. On removing the top of the 
skull in Necturus the paraphysis is seen lying beneath the pia surrounded 
by the blood-vessels which cover this part of the brain. It appears to the 
naked eye so vascular and also in sections so intimately related to the 
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