jjiZ14 NERVOUS SYSTEM OF THE HORSE 



The coeliaco-mesenteric ganglia^ are two in numl^er, 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 to 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 to 10 cm.) long. The two ganglia are united 

 by irregular connecting branches in front of and behind the anterior mesenteric 

 artery.^ Each receives the 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 small stellate posterior 

 mesenteric ganglia, which are situated at the origin of the posterior mesen- 

 teric artery. 



The coeliac plexus (P. cceliacus) consists of a felt-work of nerve-fibers in which 

 are small ganglia. It surrounds the coeliac artery and from it proceed the following 

 unpaired secondary plexuses which accompany the arterial branches: 



1. 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. 



2. The hepatic plexus (P. hepaticus) is formed by several nerves of considerable 

 size which accompanj' 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. 



3. 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. 



The anterior mesenteric plexus (P. mesentericus cranialis) is formed mainly 

 ])y branches from the posterior part of the coeliaco-mesenteric ganglia; it is con- 

 tinuous 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 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 

 hraiiclips wliicli form two fine pcriplieral plexuses in the wall of the intestine. One of these, the 

 myenteric plexus (P. myentcricus) or plexus of Auerbach, lies between the layers of the mus- 

 cular coat, and is provided witli miciroscopic ganglia. The other is in the submucous tissue, and 

 is therefore termed the submucous plexus (P. submucosus) or plexus of Meissner. 



The following paired plexust^s are derived mainly from branches of the coeliac 

 and aortic plexuses: 



1. The renal plexuses (P. reiuiles) proceed largely from the coeliaco-mesenteric 

 ganglia, but receive fibers also from the small splanchnic nerves. They enlace the 

 renal arteries and supply the kidneys. Minute renal .ganglia occur on the course 

 of the nerves along the renal vessels. 



2. The adrenal plexuses (P. suprarenales) are formed by a relatively very 

 large number of fine fibers d(M-ived in great part directly from the coehaco-mesen- 

 teric ganglia. Numerous minute ganglia occur in their meshes. 



3 a. The spermatic plexuses (P. spermatid) proceed largely from the aortic 

 and renal plexuses. Eacli aecomi^anies the corresponding (internal) spermatic 

 artery to the testicle. 



3 b. The utero-ovarian plexuses (P. ovarici) are the homologues in the female 



' 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 ganglia as well. 



^ A good preparation of tlu> 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. 



