8 Paraphysis and the Pineal Region in Necturus Maculatus 
ops it forces its way into the veins lying over this part of the fore brain, 
and the tubules, as they are given off at later stages, force their way into 
these veins, Fig. 15, forming the sinusoidal type of circulation described 
by Minot (29) and Lewis (25). From the venous circle shown in Fig. 10 
smaller vessels run down along the sides of the paraphysis and anasto- 
mose with the vessels of the choroid plexuses. A vessel also runs back to 
the epiphysis, and a larger one forward between the hemispheres. The 
circulation of this region appears at this stage to be mostly venous, as I 
could trace the arteries only to their point of entrance in the anlage of 
the skull, and the return circulation probably occurs by means of a 
minute capillary network over the surface of the brain. 
Fig. 11 is a section through the brain of an embryo of 26 mm. The 
E. 12 
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SS gg 
Fig. 11. Embryo of 26 mm. Harvard Embryological Collection, Sagittal 
Series, No. 377, Sections 125 and 126, X 63 diams. 
paraphysis here is much more developed. It inclines somewhat forward, 
and from its wide central lumen a number of tubules are given off in 
every direction. The epiphysis and the commissures show but little 
change. The striking feature of this figure is the great development of 
the plexuses. The diencephalic plexus, D. Plr., has grown through the 
mid-brain nearly to the hind-brain, and the telencephalic plexus, Tel. 
Piz., has grown downwards into the depths of the cavity of the fore brain 
towards the infundibular recess. 
Fig. 12 is a transverse section of an embryo of 26 mm., corresponding 
approximately to the line A-B, Fig. 11. The section passes through the 
epiphysis, #, and the supra commissure, S.C., just beneath it. Then 
through the diencephalic plexus, D. Plx., and that part of the cavity of 
the diencephalon between this plexus and the roof, Dien. 'The section 
