248 FEE: [Vou. IX. 
Dorsal to the epiphysis between the integument and the 
cartilaginous plate the two frontal bones meet in a median 
suture. Ventral to the distal part of the epiphysis the roof 
of the thalamencephalon is thrown into a great number of 
irregular folds (Fig. 15), and is richly supplied with blood- 
vessels so that it resembles the distal part of the epiphysis. 
This structure is usually spoken of as the choroid plexus of the 
third ventricle. 
Histology. — The histology of the epiphysis is but little 
changed from that described in the epiphysis of Salmo 25 mm. 
long. The cell boundaries are less distinct, especially those of 
the distal end. The transverse bands of radially grouped cells. 
and the fibres of the stalk are more numerous and lie close 
against each other. These fibres take a light, uniform stain 
with osmic acid and carminic acid, and show no trace of a 
myelin sheath. On leaving the stalk they pass posteriorly in 
a compact bundle along the dorsal part of the brain-roof, and 
finally blend with the fibres of the posterior commissure (Fig. 
10). Just before reaching the distal part of the epiphysis they 
spread out along the inner border of the pia-mater, and as they 
pass distally dip down toward the groups of nerve-cells. 
The boundaries of the cells of the anterior epiphysial vesicle 
have become very indistinct, but otherwise I am unable to 
detect any change from the appearance it presents in Salmo 25 
mm. long. 
Salmo, 16 cm. long (two years old). The epiphysis. — The 
growth of the epiphysis has kept pace with the growth of the 
head and with the elongation of the latter, the distal portion of 
the epiphysis has maintained its position dorsal to the cere- 
brum, where it lies in an excavation of the cartilage. At the 
same time the angle by which the distal and proximal portions 
of the epiphysis were formerly united ventrally has gradually 
been modified into a uniform curve to which the dorsal wall of 
the epiphysis now conforms (Fig. 15a). The distal part and the 
distal portion of the stalk retain the cavity, but the proximal 
portion of the stalk (not shown in the figure) has become solid. 
Owing to the further increase in the size of the epiphysis, 
and owing also to the greater number of blood-vessels on its 
