714 



THE NERVOUS SYSTEM. 



forwards in the first intercostal space and supplies the intercostal muscles. It 

 usually gives off no anterior branch to the skin of the chest and no lateral 

 cutaneous branch. 



In some cases a lateral cutaneous branch emerges from the side of the first intercostal space. 

 This may be derived from the first nerve, or it may be the intercosto-brachial nerve, i.e. the lateral 

 branch of the second thoracic nerve. In many cases an anterior cutaneous branch perforates 

 the first intercostal space and supplies the skin on the front of the chest. This branch, similarly, 

 is sometimes traceable to the second thoracic nerve. 



Communications. Besides its junction with the eighth cervical to form the 

 brachial plexus, the first thpracic nerve effects the following communications : (a) The 

 last cervical or first thoracic ganglion of the sympathetic sends a gray ramus communi- 

 cans to join the nerve on its appearance in the thorax. (6) The second thoracic nerve in 

 a majority of cases communicates with the first. This communication varies considerably 

 in size and distribution. It may reinforce the intercostal branch of the nerve, it may 

 send one branch to the intercostal portion and another to the part of the nerve joining the 



Posterior column of spinal medulla 



Posterior nerve-root 

 Anterior nerve-root | | 



Spinal ganglion .[,. 



Posterior ramus (medial branch) ^^vgtfK&MlB 



of spinal medulla 



Posterior ramus 



Posterior ramus (lateral branch)^ 

 Recurrent uieningeal branch (uniting with a sympathe 



Gray ramus communican 

 Splanchnic branch (white ram 



Anterior 



Lateral branch (posterio 

 subdivisi 



Lateral branch 



Anterior ramus 



Lateral branch (anterior 

 subdivision) 



O.-j nsrl i.ited sympathetic trunk 

 Efferent I vaso-motor) branch 



Cardinal vein 



Afferent viscero-iiihibitury 



branch 



Mesentery 



-i-Intestina 



l canal 



FIG. 622. SCHEME OF THE DISTRIBUTION OF A TYPICAL SPINAL NERVE. 



brachial plexus, or it may consist of a nerve proceeding solely to join the brachial plexus by 

 a junction in the first intercostal space with the part of the first thoracic nerve, which is 

 engaged in forming the plexus, (c) It is possible that the first white ramus communicans 

 in the thoracic region connects the first thoracic nerve with the sympathetic trunk, but 

 this is not known with certainty. 



The anterior ramus of the second thoracic nerve is of large size, though much 

 smaller than the first. It passes forwards in the second intercostal space, lying 

 at first in the costal groove, between the external and internal intercostal 

 muscles. At the level of the mid-axillary line it gives off a large lateral branch ; 

 continuing its course, it pierces the internal intercostal muscle and lies upon the 

 pleura; finally, at the lateral border of the sternum, it passes forwards in front of| 

 the internal mammary artery and through the internal intercostal muscle, and 



