DISSECTION OF THE BACK AND THORAX. Ill 



muscle ; a second spreads itself over the origin of the pulmonary artery and over the 

 right ventricle ; two other branches, grayish, plexiform, anastomose more or less between 

 the aorta and the pulmonary artery, unite under the aortic root with a nerve which 

 comes from the right side, then descend in the vertical furrow of the heart, and are 

 expended in the left ventricle ; finally, some other ramuscules, parallel to the pneumo- 

 gastric, are expended on the pulmonary artery and on the aorta." — Ghanrmu. " Traite 

 d'anatomie comparee des animaux domestiques. "] 



The left Dorsal Cord of the Syn^xithetic. — This will be seen through the 

 transparent pleura, extending beneath the costo-vertebral articulations. 

 The first portion of the cord is concealed at the outer edge of the longus 

 colli muscle, where it joins the inferior cervical ganglion. It crosses 

 the intercostal vessels superficially ; and in company Avith it, from the 

 6th intercostal space backwards, is the great splanchnic nerve. Poster- 

 iorly it passes between the psoas parvus and the left cms of the 

 diaphragm, and is continued as the lumbar cord. The cord is studded 

 with ganglia of a flattened form and greyish colour, there being a gang- 

 lion for each intercostal space. Each ganglion is placed at the posterior 

 part of the space to which it belongs, and partly on the posterior rib. 

 It is connected by an afferent filament to the intercostal nerve of the 

 same space, and from it proceed other branches, Avhich are sometimes 

 named efferent. The efferent branches from the first five or six ganglia 

 are very small, and pass to the adjacent arteries, ligaments, or vertebrae. 

 The efferent branches from the succeeding ganglia unite to form the 

 splanchnic nerves. 



The Great Splanclmic Nerve lies to the inner side of the gangliated 

 cord, as far as the 15th intercostal space. There it crosses to the outer 

 side, and is continued backwards to enter the abdomen by passing 

 between the psoas parvus and the rim of the diaphragm. In the 

 abdomen it joins the semilunar ganglion. The first efferent filament 

 contributing to the formation of the nerve comes usually from the 6th 

 ganglion, and the last from the 16th. The intermediate ganglia con- 

 tribute irregularly, some sending no branch, in which case the next 

 ganglion contributing sends a branch of more than the usual size. 



The Small Splanchnic Nerve is either the eflFerent filament from the 

 17th ganglion, or it is formed by the union of that and the filament 

 from the 16th. It passes directly to the solar, the renal, or the supra- 

 renal plexus. 



The Pulmonary Artery. This is a short vessel of enormous calibre. 

 It springs from the conus arteriosus of the right ventricle ; and passing 

 in front of the common aorta, it gains its left side, crosses the root of 

 the posterior aorta, and divides behind it into a right and a left branch, 

 one for each lung. Each of these enters the root of the lung and 

 divides. As the trunk of the pulmonary artery rests on the root of the 

 posterior aorta, it is connected to it, in the adult, by a fibrous cord 

 which is the remains of the ductus arteriosus— o. vessel which in the 



