ON THE SPINAL MARROW AND SPINAL NERVES. 189 
hip-joint and the tuberosity of the ischium, enters deeply into 
the haunch ; and having given branches to the biceps, the se- 
mitendinosus and the semimembranosus, divides into the three 
popliteals. The first of these answers to the ulnar nerve of the 
fore extremity; the second feeds the gastrocnemii, the flexors of 
the foot, and reaches to the stifle-joint; and the third, after 
sending branches to the semimembranosus, the gastrocnemius 
externus, the flexor metatarsi, and the extensor pedis, pursues 
its way down the leg, and becomes at length a subcutaneous 
nerve, terminating on the pastern. 
The fifth lumbar nerve sends a considerable branch to help to 
form the gluteal; but the main substance of it is derived from 
the first sacral. It is expended on the glutseus maximus. 
I have no material difference to point out in the distribution 
or function of the lumbar nerves in our other domesticated 
quadrupeds. 
The Sacral Nerves .—Besides contributing to form the sciatic 
and gluteal nerves, the first of the sacral nerves anastomoses 
with the second lumbar. The second ramifies posteriorly among 
the muscles of the tail; the third gives branches to the muscles 
of the haunch; the fourth supplies the bladder, and rectum, 
and perinseum; and the ffth belongs to the muscles of the tail. 
All these are composed of branches of the inferior divisions of 
the sacral nerves, and which likewise communicate with the 
great organic nerve, and with the lumbar nerves. The superior 
divisions, as in the dorsal and lumbar nerves, supply the dense 
mass of muscle above, or penetrate through it, and become sub¬ 
cutaneous nerves. 
The Cauda Equina .—The spinal chord had begun rapidly to 
diminish at the last lumbar vertebra; and at the second of the 
sacral bones it may be said to end. We can trace a little pvra- 
midical point in the centre which is its apparent termination. 
This bulb, however, is surrounded by numerous nervous chords, 
forming at first a bundle of prolongations or large filaments more 
bulky than the chord from which they sprung, but gradually 
diminishing in size and in number, and ceasing altogether about 
the fourth caudal vertebra. The three last sacral nerves are form¬ 
ed from these chords, which, like those from the spinal marrow 
itself, are perfect nerves of sensation and voluntary motion. The 
sacral nerves, however, issue by two distinct foramina from the 
spinal canal ; the superior penetrate at once into the muscles 
above; the inferior escape into the pelvis; but they are not nerves 
of different character or function, for after the motor portion had 
joined the sensitive, and the compound nerve was formed, the 
VOL. vii. C c 
