On either side, and at some little distance from
the great median fissure, two superficial channels
may be observed on the dorsal surface of the
human spinal cord (pi. i. fig, 5, a — a.) They ex-
tend as far as, or a little way beyond, the first
dorsal vertebra. The two bands between the
median and these superficial fissures, are de-
veloped at the earliest period; their structure is
even complete, when the rest of the spinal cord
is still a grayish and pulpy mass. The bands on
the external edges of the dorsal and abdominal
median fissures, appear, in general, to attain ma-
turity of structure before any of the lateral masses.
By opening the mesial abdominal fissure, and
stripping off the vascular tissue, the nervous fibres
will be seen running lengthwise and parallel to
the lateral bands, (pi. i. fig. 6;) but in the dorsal
cleft, they will be found descending perpendicu-
larly from the surface towards its bottom. (PI. i.
fig. 7.)

The structure of the apparatus of union has not
the same appearance at the bottom of both fissures.
I If the edges of the one on the dorsal aspect be
I gently separated, two white bands will be disco-
I vered running lengthwise (pi. i. fig. 7, 3 — &), almost
1 as occurs in the middle line of the great cerebral
I commissure (raphe of the corpus callosum) ; a(^
I the bottom of the abdominal fissure, on the con-
B trary, filaments will be observed running trans-
■ versely from the sides towards the median line.
