1884.] NATURAL SCIENCES OP PmLADELPHIA. 213 



opt. — Optic lobe. 



p. — ^Porta, Foramen of Munro. 



pes. — Postcommissura, posterior commissure. 



p. 7iph. — Posterior lobe of hypophysis. 



pi. — Pia, pia mater. 



ppd. — Post-pedunculus, posterior peduncle of cerebellum. 



pp. — Pars peduncularis of Mesencephalon. 



pre. — ^Procoelia, lateral ventricle, 



pr. cs. and pr. cs'. — Prsecommissura, anterior commissure, lower and upper 



divisions. 

 pr. eph. — Processus pinealis, the epiphysial stalk. 

 pr. px. — Proplexus, the choroid plexus of the lateral ventricle. 

 pr. pd. — Pi sepedunculus, anterior peduncle of cerebellum. 

 r. eph. — Recessus infra-pinealis, the opening of the epiphysial cavity into 



the diacoelia. 

 rhen. — Section of olfactory lobe. 

 rst. — Restiform tract. 



8C8. — Supracommissura, commissure of the habenulge. 

 scm. — Superior commissure of the infundibulum. 

 spx. — Supraplexus (formerly considered the epiphysis), the upper portion 



of the vascular plexus of the prosocoelia. 

 spd. — Supra-pedun cuius, fibres passing from the cerebellum into the optic 



lobe. 

 t. — Terma, lamina terminalis. 



Figures 1, 2, 3. Dorsal, ventral and lateral aspects of the brain of Meno- 

 poma AUeghense, enlarged five diameters. The whitish band stretching 

 across the infundibulum, in front of the hypophysis, probably consists of 

 the inferior infundibular commissure. In the dorsal aspect of the fresh 

 brain, the position of the epiphysial process, is marked by an oval 

 transparent area, in front and behind which, the supra- and post- 

 commissurse shine through. This area is undoubtedly contracted by 

 reagents. The natural backward direction of the cerebellum is also 

 altered, so that it hangs beneath the optic lobe. 



Figure 4. Longitudinal vertical section of the brain of Menopoma, in 

 a median plane as far forwards as the terma, and in front of this through 

 the centre of the right hemisphere ; enlarged sixteen diameters. The 

 dotted ellipse indicates the position of the porta, or foramen of Munro. 



Figure 5. The diatela, or roof of the third ventricle of the brain of Rana 

 Mugiens. This figure represents the long tubular epiphysial process, 

 composed of two or three rows of cells, mostly enveloped by the pia 

 and extending forwards above the supracommissura. The inner layer 

 cells send short processes into the persistent cavity of the epiphysis, 

 and the cavity is filled by a highly transparent meshwork, which may 

 simply consist of coagulated fluid. The opening into tlie diacoelia, 

 r. eph., is doubtful. The lines {fi.), indicate a number of nerve 

 fibres, which apparently extend to the base of the epiphysial process. 



