THORACIC NERVES 177 



Third cervical nerve is called the least occipital nerve, and 

 is rather small, but its distribution is similar to that of the 

 posterior divisions of the other spinal nerves. 



The anterior divisions of the rest supply the trunk and the 

 limbs. They form what are called plexuses, which are groups 

 of nerves joined up together. There are five plexuses viz. r 



Cervical plexus, formed by cervical nerves 1, 2, 3, and 4, 

 supplies the muscles and skin of the neck. 



Brachial plexus, formed by cervical nerves 5, 6, 7, 8, and a 

 branch of the first dorsal nerve, supplies the upper limb. 



Lumbar plexus, formed by a branch of the twelfth dorsal 

 nerve, lumbar nerves 1, 2, 3, and a branch of the fourth lumbar 

 nerve, supplies the anterior, inner, and outer surfaces of the 

 thigh. 



Sacral plexus, formed by lumbar nerves 4 and 5, and sacral 

 nerves 1, 2, 3, supplies buttock, posterior surface of thigh and 

 leg and foot. 



Pudendal plexus, formed by a branch of the third sacral 

 nerve, sacral nerves 4 and 5, and the coccygeal nerve, supplies 

 the perineum. 



The anterior divisions of the twelve dorsal or thoracic nerves 

 supply the skin and muscles on the anterior and lateral surfaces 

 of the trunk. The first eleven are intercostal, the twelfth lies 

 below the last rib. 



The Intercostal Nerves are much alike in their course 

 and distribution, but some of them differ slightly from the 

 others. 



A typical thoracic nerve enters the posterior end of the 

 subcostal groove, and lies between the intercostal muscles. 

 Coursing forwards, it pierces the internal intercostal muscle 

 about the middle of the chest wall, and lies on the pleura. Near 

 the middle line it pierces again the internal intercostal musck 

 and the aponeurosis of the external intercostal, and supplies 

 the skin over the front of the chest corresponding to the an- 

 terior half of the space to which it belongs. 



Branches. Cutaneous, a lateral cutaneous branch is given off 

 in the mid-axillary line to the skin over the space to which it 

 belongs ; it divides into anterior and posterior branches. 



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