ON THE SPINAL MARROW AN1) SPINAL NERVES. 187 
It now rapidly diminishes, and becomes little more than a round 
chord; but still a succession of nerves from above and below are 
given out from it, opposite to each of the articulations of the 
spine, yet with this singular circumstance, not existing however 
to so great an extent in the brute as in the human being, that 
while the origins of the cervical nerves are opposite to the fora¬ 
mina through which they escape, the posterior dorsal and the 
lumbar nerves spring from portions of the spinal chord anterior 
to these foramina, and increasingly so, and therefore they run a 
certain way along the side of the spinal chord, before they escape 
from the canal. Do they thus receive any minute filaments or 
influence from the lateral columns of the spinal chord? This is 
worth observation and inquiry. 
The Intercostals .—There are eighteen pairs of dorsal nerves. 
They are smaller than the cervical nerves, and present fewer 
anastomoses, and even fewer ramifications; for there is less mus¬ 
cular substance to supply, and far less muscular action. Each 
dorsal nerve, as it escapes, divides into two branches. The in¬ 
ferior one, after giving a branch to the panniculus carnosus, and 
to the integument, shelters itself with the bloodvessels in a 
sulcus under the posterior edge of the rib behind which it escapes 
from the spinal canal: as it passes, it gives minute ramifications 
to the muscle between that and the next rib, and then, in the 
anterior ribs, expands itself on the muscles of the sternum; while 
the nerves of the posterior ribs, after supplying the intercostal 
muscles, send their ultimate fibrils to the internal oblique and 
recti-abdominal muscles. These are plainly respiratory nerves, 
and we shall have reason to suspect that they proceed from, al¬ 
though they have not been actually traced to, the lateral column 
of the spinal chord. At all events, each intercostal nerve anas¬ 
tomoses with the great organic, and forms with it a ganglion. 
The superior branch of the nerve turns upwards, becomes 
deeply buried in the muscles of the back, and gives filaments to 
the serrati, the rhomboides, the trapezius, the latissimus dorsi, 
the quadratus, the psoas magnus, the iliacus internus, the su¬ 
perior abdominal muscles, and, in fact, all the muscles of the 
back and loins. 
Comparative View oj the Dorsal ^Serves .—The only important 
difference in the dorsal nerves of other domesticated animals is 
in their number, and that corresponding with the number of the 
ribs. In the ox, the sheep, and the dog, there are but thirteen ; 
there are fourteen in the hog; and in the bird they seldom ex¬ 
ceed seven or eight. 
The Lumbar Serves. —There are five lumbar vertebrae, and a 
corresponding number of nerves. The spinal chord is now be- 
