DISSECTION OF THE BACK AND THOKAX. 113 



The inferior cervical ganglion detaches a slender cardiac nerve which, 

 after throwing off some twigs to the arteries in the anterior mediastinum, 

 passes downwards and backwards to the left auricle. 



The left Dorsal Cord of the Sympathetic. — This will be seen through 

 the transparent pleura, extending beneath the costo-vertebral articula- 

 tions. 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 with it, 

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

 Posteriorly it passes between the psoas parvus and the left crus 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, which 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 Splanchnic Nerve lies to the inner side of the gangliated 

 cord, as far as the 15th intercostal space. Thrre 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 efferent 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 Aeteey. 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 — a vessel which in the 

 foetus brings the two arteries into communication. The pulmonary 

 artery conveys venous blood to the lungs to be purified. 



The Common Aoeta. This is the primary trunk of the systemic 



