No. 2.] EPIPHYSIS OF TELEOSTS AND AMIA. 243 
= 
epiphysis. Its histology, as well as its method of development, 
is, however, very different from that of the epiphysis, and will 
be spoken of in detail in another place. 
Lying close against the anterior border of the stalk of the 
epiphysis and in the dorsal part of the brain-roof is a small 
column of transverse fibres, the superior commissure (Fig. 11, S). 
Gottsche (35, p. 455) speaks of this commissure in Teleosts 
as commissura tenuissima. Stannius ('53, p. 129) finds it in 
Pleuronectidae, but fails to find it in Cottus scorpius, while 
Rabl-Riickhard (82) in his work on Salmo does not mention 
it. Ahlborn (83) describes it in Petromyzon ; Balfour ('78) 
finds it in Selachians. Osborn (gg) finds it in Amphibia and 
calls it superior commissure. The fibres of this commissure 
may be traced on either side to the structures described by Rabl- 
Riickhard as probably homologous with the ganglia habenulae 
of other forms. These fibres are first seen at the time of the 
formation of the epiphysial vesicles in both Salmo and Coregonus 
albus. 
The epidermis just dorsal to the epiphysis consists of several 
layers of columnar cells and of scattered goblet cells opening 
to the external surface. Between the epidermis and the epi- 
physis is a plate of undifferentiated tissue into which the distal 
part of the epiphysis projects so as to lie with its distal end 
very close to the external epithelium. 
Histology. — All the cells of the proximal part of the epi- 
physis and most of those of the distal part are ovoid and 
arranged radially to the cavity of the epiphysis. Scattered 
among the ovoid cells of the distal part are a few cells, the 
outer ends of which are pointed. In the posterior part of the 
dorsal wall some of these cells (Fig. 11, vv. CZ.) are arranged 
in radial groups, each of which is separated from adjacent 
groups by a few ovoid cells with ovoid nuclei. The pointed 
ends of all the cells in each group are approximated and directed 
toward the outer surface. This grouping of cells is more evident 
in Salmo 25 mm. long, and is described in detail under that 
head. A few large cells with distinct cell boundaries, and 
showing certain stages of karyokinesis, are usually found in 
the distal part of the epiphysis. 
