mo RACK' XENVKS TUD 



THORACIC NERVES 



The sinuller part of the first thoracic nerve and tlir second to tlic elcventli 

 thoracic nerves follow the contour nf tlic hody wall in the intervals l)etween the 

 rihs, and are therefore termed intercostal nerves. The twelfth thoracic nerve 

 j)ursues a parallel course to the others, below the twelfth ril). Each of the inter- 

 costal nerves is accompanied by an intercostal artery and vein. These vessels are 

 l)laced, inniiediately above the nerve, in the groove at the lower border of the rib. 

 The twelfth thoracic nerve is accompanied by the first hinibar artery. Each 

 thoracic nerve is joined, near the head of the rib, by two rami communicantes 

 from the gangliated cord of the sympathetic. The first and last thoracic nerves 

 reijuire separate di'scrii)tion. The remaining ten nerves fall naturally into an u[>]Kr 

 and a lower group. The members of the upper group (the second to the sixth ) 

 run between the ribs as far as the margin of the sternum. The mem1)ers of the 

 lower group ( seventh to eleventh ner\'es) lie for a i)art of their course l)etween the 

 layers of the al)dominal wall, the extent of the abdominal distribution increasing 

 from the liighest to the lowest member of the series. 



A. First thoracic nerve. — The greater part of the first thoracic nerve crosses 

 the neck of the first rib to join the brachial plexus, as already descril)ed. The 

 smaller part, about one-fifth of the entire nerve, runs for about two inches in 

 contact with the under surface of the first rib between the bone and the pleura, and 

 tiien enters the cellular interval between the external and internal intel-costal 

 muscles. For the remainder of its course it corresponds to the upper intercostal 

 nerves in its distribution, but it does not usually give a lateral or an anterioi- 

 cutaneous branch. 



Variety. — In some cases a lateral cutaneous nerve arises from the first intercostal nerve. It 

 ...ay be of" small size, but is sometimes as large as an ordinary intereostu-liunieral nerve. It 

 LMjmmuiiieates with the intercostohumeral nerve and with the nerve of Wri.sberg. 



B. Upper intercostal nerves. — The second, third, fourth, fifth, and sixth inter- 

 costal nerves, after receiving connnunications from the sympathetic, are directed 

 outwards in the intercostal spaces in front of the posterior intercostal membrane, 

 between that membrane and the jdeura. They then enter the interval between the 

 external and internal intercostal muscles, and follow the curve of the thoracic wall 

 l)etween these muscles as far as the mid-axillary line, and then, taking a dee])er 

 position, they run through the fibres of the internal intercostals as far as the junction 

 of the bony parts of th(! ribs with their cartilages. Hence they pass forwards on the 

 deej) surface of the internal intercostal muscles, lying on the pleura and on the slips 

 of the triangularis sterni, and cross in front of the internal mammary vessels. 

 Lastly, they bend forwards and pierce the internal intercostals, the anterior inter- 

 costal membranes and the pectoralis major, and terminate as the anterior cutaneous 

 nerves of the thorax. In this course they give off nuiscular branches to the 

 l(>vatores costarum, serratus posticus superior, external and internal intercostals, 

 and triangularis sterni. Il^ach nerve also gives off two cutaneous branches — 

 namely, the lateral and ant(n"ior cutaneous nerves of the thorax. 



The lateral cutaneous nerves of the thorax ])ierce the external intercostal 

 nmscles, and divide into anterior and j)o.steriitr branches. These l)ranches pa.ss 

 l)etween the digitations of the serratus magnus, and are separated by an interval of 

 about half an inch when they appear on the superficial surface of that muscle. 

 The anterior branches run forwards, cross the lower border of the great pectoral, 

 and supi)ly the integuments which cover the lower and outer jtortion of that muscle, 

 and give twigs to the mannnary gland. They increase jirogressively in size from 

 above downwards. In the case of the second lateral (nitaneons nerve, the anterior 

 Itranch is usually wanting. The posterior branches turn backwards, and su]>ply 

 the skin covering the outer ])art of the latissinuis dorsi and the infericn- angle of 

 the scapula. The lateral cutaneous l)ranches of the second and third intercostal 

 nerves are larger than the others, and reijuire separate notice. The lateral cuta- 



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