40 Journal of Comparative Neurology. 



appearance of an evagination by the velum. The last structure 

 has been recognized in Amphibia and Reptilia and appears of 

 morphologic value. By some it has been assumed as the 

 boundary between the prosencephal and diencephal. In Amia 

 it passes ventrally immediately caudad of the cerebral lobes, 

 which slope at their caudal end and hence give the dorsal sack 

 more volume. The velum is attached to the recurved edge of 

 of the cerebral lobes and therefore the same condition of the 

 latter would render greater the extent of the velum. The 

 prominence of the velum in Ganoids may be in part due to the 

 recurved condition of the cerebral lobe at its caudal end. 



The membranous roof caudad of this fold has a modifica- 

 tion which when first observed was rather startling. There oc- 

 curs on each side a lateral extension of the cavity just caudad 

 of the velum, forming diverticula which divide into two limbs, 

 caudal and cephalic. The latter extends cephalad just ventrad 

 of the recurved edge of tfie cerebrum as far as the olfactory 

 lobes ( Figs. 3, 4). The caudal limb is even more extensive: 

 closely applied to the side of the mesencephal, it reaches 

 the cerebellum and the ventral portion passes farther caudad 

 encountering the fifth nerve which divides it into a short 

 dorsal portion and a longer ventral one, which in some brains 

 at least attains the level of the ninth nerve, closely applied to 

 the ventral aspect of the oblongata. 



Lepidosteus resembles Anna closely. The relations are 

 somewhat modified however by the different shape of the cere- 

 bral lobes. These do not slope away at their caudal ends 

 which are more closely applied to the geminums and more 

 nearly perpendicular to the dorsal surface. The recurvature of 

 the dorsal edge is not so great ( fig. 2 ). All this limits the 

 capacity and extent of the dorsal sack and the size of the 

 velum. The caudal extension of the dorsal sack upon the mes- 

 encephal is somewhat greater than in Amia. The epiphysis 

 in Lepidosteus is in its proximal part enveloped in the dorsal sack 

 and extends caudad to bend cephalad forming a V. In Amia 

 the epiphysis first passes cephalad then caudad and again ceph- 

 alad, performing thus a sigmoid curve. The lateral diverticu- 



