No. 1.] AMPHIBIAN BRAIN STUDIES. 55 
leaving a slit-like, oval or triangular space, in the centre of 
which lies the proximal portion of the pineal stalk or proces- 
sus pinealis, fz. Close behind this a white or grayish streak 
represents the postcommissura. Upon the floor of this 
segment is an oval space, bounded by a whitish area which rep- 
resents the recessus opticus, or proximal portion of the 
primitive optic stalk, which recess in WVecturus and Proteus ex- 
tends directly into the centre of rudimentary optic nerve. There 
is a striking similarity, which may be merely superficial, between 
this area and that surrounding the processus pinealis. The 
most prominent features of the floor are the infundibular lobes, 
probably homologous with the lobi inferiores of the Tele- 
osts, which terminate in the large hypophysis. These lobes 
extend anteriorly into the flattened floor of the 3d ventricle, 
and laterally into the sides of the thalami. Above them, the 
cerebral peduncles diverge around the infundibulum into the 
lower portions of the thalami. 
The roof of the Mesencephalon is distinguished by a 
longitudinal grayish line, probably caused by the thinning of 
the wall; on either side of this is a whitish tract the meaning 
of which is unknown. Posteriorly the roof thins out into the 
valvula, a triangular area from which arises the 4th nerve. 
This nerve is apparently atrophied in Proteus. The slender 
band representing the cerebellum extends across behind this, 
continuous at the sides with the lateral fold of the medulla. 
The figures do not represent the actual condition of the 
Metencephalon, since the metaplexus has been removed. 
The metacoele, or 4th ventricle, is shallow and widely open 
in the Uvodela, and varies considerably in shape. In Proteus 
the lateral edges are approximated opposite the roth nerve. 
On either side of the longitudinal sulcus, in the centre of the 
floor, are observed two long white tracts shining through and 
giving off lateral branches opposite the exit of the VII., VIII. 
nerves. This tract is the posterior longitudinal fasci- 
culus, and can be very clearly seen in well-preserved speci- 
mens. On the ventral surface is seen the anterior sulcus con- 
tinuous with the fissure of the cord. It diverges at two points 
in the medulla of Proteus, the meaning of which is not known. 
I have not observed in the floor of the 4th ventricle of the 
Urodela any trace of the foldings seen in the medulla of Rana 
