132 | PECK. [Vot. III. 
The central lumen or canal of the cord is seen to be very promi- 
nent at this point, and is surrounded by a dense row of nuclei, 
which are those of the epithelium lining the canal. The exact 
nature of the other mass of nuclei that are collected within the 
investing membrane is not easy to determine. Some of them are 
quite large and show a distinct nucleolus, a few may be from the 
gray matter, and some connective tissue nuclei. A neuroglia 
also exists to some extent, — enough to form a kind of matrix 
for the nuclei. As the filum passes forward, the same general 
structure is seen, but its actual size is much increased, the 
nuclei becoming fewer, and the neuroglia consequently more 
distinct. Thus Fig. 7 represents a section taken beyond the 
coccyx on the posterior face of the last free vertebra; z.e., in the 
anterior part of s, in Fig. 2. The filum has increased in size, 
and the lumen is lined by a row of columnar nucleated cells, 
while in the other parts the nuclei are less thickly distributed 
than in the former section. The dura mater investment lines 
the neural arch cavity, and the pia mater closely invests the 
filum itself, being thicker upon the lower side. It is from 
this lower side of the pia mater investment that connective 
tissue processes are given off which go out to the dura mater 
and serve to support the cord in place. In this region they 
are not numerous, but they are seen in serial sections attached 
to the dura mater and to the pia mater; they are sometimes 
oblique, and are then to be carefully distinguished, when viewed 
under low powers, from nerves lying in the cavity. Blood- 
vessels are now abundant in the dura mater, and smaller ones 
in the pia mater. Passing forward into the next anterior 
space (ss, Fig. 2) and selecting a section well forward so as to 
include the position of outgoing nerves, the structures take the 
form represented in Fig. 8. The connective tissue arch between 
the including vertebrae becomes somewhat broken through in 
part, and allows the exit of blood-vessels that pass to parts be- 
neath ; but in this, as in all the sections of this vertebra, —cut- 
ting anteriorly, —no pair of nerves lying near the cord is cut. 
The lumen of the cord —still lined by the nucleated cells — is 
becoming relatively smaller, the size of the filum terminale itself 
is increased, and together with the investing membranes takes 
on more of the characters of the cord proper. A section in the 
next intervertebral space (s;, Fig. 2) includes the last pair of 
