54 
GEORGE E. N[CHOLLS. 
dilated to partly enclose the sinus terminalis. Above, 
its tneningeal sheath is pi'otected only by the skin, with 
which it lies intimately in contact. Eemoval of the skin 
appears invariably to involve the hinder part of the dural 
envelope of the spinal cord also, and, as a consequence, the 
sinus terminalis, of whose wall that envelope forms an in- 
tegral part. If, however, the skin be not I’emoved, tlie whole 
tail becomes greatly crumpled and folded during the processes 
of paraffin embedding, owing to the considerable shrinking of 
the skin, which itself becomes at the same time very tough 
and leathery. I’hus, in those series in which the end of the 
spinal cord had been dissected out (specimens A, B) or in 
which the skin had simply been removed (specimen C), the 
sinus terminalis was wanting. On the other hand, in 
both of the two series of sections (specimens D, E) in which 
the intact tail region was cut sagittally, it came about that the 
sinus ter miual is, although preserved entire, was unavoid- 
ably cut slightly obliquely to the vertical longitudinal plane 
desired. 
A photomicrograph of a section through the sinus ter- 
minalis of each of these two latter (d, e) has been repro- 
duced (figs. 12, 13, s.t.), while fig. 40 is a composite drawing 
obtained by superposing camera drawings of four or five 
consecutive sections of the series through the tail of 
.specimen D. 
The sinus (ventriculus) terminalis in Petromyzou 
fluviatilis may be seen in both of my complete series as a 
somewhat ovoidal space formed by the widening out of the 
hinder end of the canalis centi-alis. By Studnicka (’95a) 
it is said to be invariably present in both P. fluviatilis and 
P. planeri ; Retzius (’95) says simply that in P. fluviatilis 
it frequently occurs. 
The anterior part of the wall of this space is formed by the 
ependymal epithelium of the filum terminale. At about 
its middle, however, this fails, so that posteriorly the sinus 
terminalis is bounded only by the confluent connective 
tissue envelopes of the spinal cord (Fig. 40). The canalis 
