THE THORACIC NERVE* 



931 



TABLE SHOWIM; TIII-: KKI.VHONS OK TIIK Mi -< LES OK THK L'ITLK EXTKK.MITY TO 

 THE CERVICAL XKH\ T.S- -(Continued) 



SC. 



7, 8 C., and IT. 



8 C. and 1 T. 



XI:K\KS CONTIHHVTIXC. Mus< i 



5, 6, 7, and 8 C Pectoralis major 



Dorsal inteross. 

 Palmar 

 Add. pollicis 

 '" pollicis trans. 

 Flex, pollicis brev. 



(deep) 



I'ertoralis minor 

 Flex, digit, subl. 

 Lumbricals 

 Flex, carpi uhiaris 

 " digit, prof. 

 " pollicis long. 

 Pronator quadratus 



.\i:u\ i:s ID Mi SI-I.KS. 



F.xt. and int. tint, thoracic 

 t'lnar 



Int. ant. thoracic 



Median 



" and ulnar 

 rinar 



and median 

 -Median 



THE THORA CIC NER VES 



The anterior primary divisions of the thoracic nerves, with the exception 

 of the first, retain, in the simplest form, the characters of anterior primary divisions 

 of the typical spinal nerve. They do not form -plexuses, but remain distinct from 

 each other. Each divides into an easily recognisable lateral or dorsal and anterior 

 or ventral branch (figs. 685 and 686) , and they are not distributed to the limbs. The 

 first, second, and last thoracic nerves, on account of their peculiarities, require separate 

 description. The remainder are separable into two groups, an upper and a lower 

 The upper group consists of four nerves, the third to the sixth inclusive, which are 

 distributed entirely to the thoracic wall. The lower group contains five nerves, the 

 seventh to the eleventh inclusive, which are distributed partly to the thoracic and 

 partly to the abdominal wall. The upper group is therefore purely thoracic in dis- 

 tribution, and the lower thoraco-abdominal. 



The first thoracic nerve is connected with the first thoracic sympathetic ganglion, 

 and it frequently receives a communication from the second nerve. It is distrib- 

 uted chiefly to the upper limb. Opposite the superior costo-transverse ligament 

 of the second rib it divides into a larger and a smaller branch; the larger passes 

 upwards and outwards, between the apex of the pleura and the neck of the first 

 rib, and on the outer side of the superior intercostal artery, to the root of the neck, 

 where it joins the brachial plexus. The smaller branch continues along the inter- 

 com al space, below the first rib and between the intercostal muscles in which, as a 

 rule, all its fibres terminate. However, in some instances it gives off a lateral cutan- 

 eous branch which connects with the medial brachial (lesser internal) cutaneous nerve 

 and with the intercosto-brachial nerve in the axillary fossa; and occasionally it 

 terminates in an anterior cutaneous branch at the anterior extremity of the first inter- 

 costal space. 



The second thoracic nerve, as it lies between the pleura and the superior costo- 

 transverse ligament of the third rib. gives a branch to the first nerve, then it pierces 

 the posterior intercostal membrane and passes' between the external and internal 

 intercostal muscles in the second intercostal space. In the posterior part of the space 

 it sends branches backwards, through the external intercostal muscle, to supply the 

 second levator costa 1 and the serratus posterior superior, and then it divides into a 

 luti nil and an (interior branch. The two branches run forward together to the mid- 

 axillary line, where the lateral branch pierces the external intercostal muscle and 

 passes between two (limitations of the serratus anterior (inairnus) into the axillary 

 fossa; the anterior branch enters the substance of the internal intercostal muscle. 



