THE ABDOMINAL AND PELVIC PLEXUSES 833 
The cceliaco-mesenteric ganglia (G. cceliaco-mesenterica)! are two in number, 
right and left. They are situated on each side of the aorta, in relation to the origin 
of the coeliac and anterior mesenteric arteries. The right ganglion is concealed by 
the posterior vena cava; it is irregularly quadrilateral and is about two inches (4- 
6 cm.) in length. The left ganglion is largely covered by the left adrenal; it is 
narrower than the right one and is three or four inches (ca. 8-10 cm.) long. The 
two ganglia are united by irregular connecting branches in front of and behind the 
anterior mesenteric artery.” Each receives the great splanchnic nerve of its own 
side and branches from the dorsal cesophageal continuation of the vagus nerves. 
Branches from the ganglia and the cords which connect them pass back to the 
posterior mesenteric ganglion which is situated at the origin of the posterior mesen- 
teric artery. 
The following unpaired plexuses proceed from the cceliac plexus and cceliaco- 
mesenteric ganglia: 
1. The abdominal aortic plexus (P. aorticus abdominalis) occurs along the 
abdominal aorta. It is connected with the renal plexuses and behind with the 
pelvic plexus. It receives filaments from some of the sympathetic lumbar ganglia. 
2. The gastric plexus (P. gastricus) enlaces the gastric artery and divides like 
the artery into two parts, forming the anterior and posterior gastric plexuses. 
These receive branches of the vagus nerves. 
3. The hepatic plexus (P. hepaticus) is formed by several nerves of consider- 
able size which accompany the hepatic artery and the portal vein. It receives 
fibers from the left vagus, ramifies in the liver, and gives off branches which 
accompany the collateral branches of the hepatic artery and supply the areas in 
which these vessels are distributed. 
4. The splenic plexus (P. lienalis) resembles the preceding in its arrangement. 
In addition to its terminal branches to the spleen it gives collateral twigs to the 
pancreas and the left part of the greater curvature of the stomach. 
5. The anterior mesenteric plexus (P. mesentericus cranialis) is formed 
mainly by branches from the posterior part of the cceliaco-mesenteric ganglia; it 
is continuous with the cceliac plexus in front and the posterior mesenteric behind. 
Tt surrounds the anterior mesenteric trunk and its branches, and supplies the viscera 
to which these vessels are distributed. 
The posterior mesenteric ganglion (G. mesentericum caudale) is unpaired; it 
is irregularly stellate, and is situated on the origin of the posterior mesenteric 
artery. It is connected with the cceliaco-mesenteric ganglia by anastomosing 
branches which concur in the formation of the aortic plexus. Two or more pairs 
of nerves proceed from it posteriorly. One of these, the internal spermatic nerve 
(N. spermaticus internus), accompanies the spermatic artery to the spermatic cord 
and testicle in the male; in the female it goes to the ovary, uterine tubes, and 
adjacent part of the uterine horn. These concur in the formation of the spermatic 
and utero-ovarian plexuses. The other branches from the ganglion pass back to 
the pelvis ventral to the great vessels and concur in the formation of the pelvic 
plexuses. 
The posterior mesenteric plexus (P. mesentericus caudalis) accompanies the 
artery of like name in its distribution. 
The secondary plexuses which accompany the branches of the mesenteric arteries give off 
branches which form two fine peripheral plexuses in the wall of the intestine. One of these, the 
myenteric plexus (P. myentericus), or plexus of Auerbach, lies between the layers of the mus- 
cular coat, and is provided with microscopic ganglia. The other is in the submucous tissue, and 
is therefore termed the submucous plexus (P. submucosus) or plexus of Meissner. 
1Tt has been customary to designate these in veterinary works as the semilunar or cceliac 
ganglia, but in the horse they evidently include the anterior mesenteric ganglia as well. 
* A good preparation of the ganglia in the horse is often difficult to obtain on account of 
aneurysm of the artery and the formation of a quantity of connective tissue about it. 
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