:!22 Journal ok Cfmi'AHATnE NEi'noLO(;v. 



contact with the palHum as far cephalad as the exit of the 

 olfactory crura, then turns dorsad to the roof of the cranial 

 cavity. The diameter of the tube is about .i mm. at the 

 base, but increases slightly as it passes out. About the base 

 of tiic epiphysis the membranous roof of the third ventricle 

 is inflated dorsad to form a small closed sac which is nearly 

 spherical and about i mm. in diameter. This represents the 

 dorsal sac, which is so conspicuous a feature in many fish 

 brains. In this case it is entirely obscured from view in the 

 brain before dissection bv the over-arching cerebellum. The 

 walls of this sac are intricately plicated, the folds embracing 

 the base of the epiphysis and forming what has been pre- 

 viously mentioned as the homologuc of the choroid plexus. 

 The epiphysis is related to the roof of the cerebral ventricles 

 cephalad in essentially the same way; /.c, it is imbedded in 

 the pallium and surrounded by it. Thus morphologically the 

 dorsal sac is produced forward nearly to the end of the 

 cerebrum, though its cavity has been all but obliterated. 



On the ventral aspect the hypoaria and hypophysis cover 

 nearly the entire cephalic portion of the brain. Each hypo- 

 arium is a pear-shaped body, flattened dorso-ventrally, with 

 the smaller end directed cephalad and the more concave 

 surface mesad. At the cephalic end of each hypoarium is a 

 small tubercle lying immediately ventrad to the lateral 

 portion of the optic nerve at its exit from the brain. In the 

 adult the hypoaria are divaricated cephalad by the cinereum. 

 This body is cordate with the apex directed caudad, and is 

 somewhat over half as long as the hypoaria. Attached to its 

 apex and lying in the narrow cleft between the caudal ends 

 of the hypoaria is the saccus vasculosus, which, in large 

 brains, sometimes attains a diameter ot 3 mm. This is a 

 membranous sac, the base of which, lying between the 

 hypoaria, is filled with a vascular plexus, resembling in 

 structure the vascular portion of the epiphysis of higher 

 animals. The more expanded portion, overlying the larger 

 ends of the hypoaria, is discoid or sub-spherical, more delicate 



