THE ABDOMINAL AND PELVIC PLEXUSES 833 



The coeliaco-mesenteric ganglia (G. coeliaco-mesenterica)i 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 oesophageal 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 cojliaco- 

 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 i-lexus (P. mesentericus cranialis) is formed 

 mainly by branches from the posterior part of the ccfiliaco-mesenteric ganglia; it 

 is continuous with the coeliac plexus in front and the posterior mesenteric behind. 

 It 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 coeliaco-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. 



^ It has been customary to designate these in veterinary works as the semilunar or coeliac 

 ganglia, but in the horse they evidently include the anterior mesenteric gangha 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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