1 66 THE POCKET ANATOMY 



forearm, where it passes deep to extensor longus pollicis to 

 reach the interosseous membrane, on which it lies, as far as 

 the wrist ; it there ends in a gangliform enlargement, from 

 which there are given off filaments to the ligaments, etc. 

 Supplies supinator brevis, extensores carpi radialis brevior, 

 communis digitorum, minimi digiti, carpi ulnaris, ossis meta- 

 carpi pollicis, longus and brevis pollicis, and indicis. 



NERVES OF THE TRUNK. 



DORSAL : twelve in number. The ist comes out between 

 the ist and and dorsal vertebrae, and the greater part joins 

 the brachial plexus. The last nerve emerges from between 

 the i ath dorsal and ist lumbar vertebrae. Each nerve at its 

 exit from the intervertebral foramen divides into an anterior 

 and posterior primary division. The ist and I2th nerves, 

 however, require a separate description. 



The POSTERIOR* PRIMARY DIVISIONS, or dorsal branches, 

 pass backwards between the transverse processes and divide 

 into external and internal branches, which emerge on either 

 side of the middle division of the erector spinse (longissimus 

 dorsi), and supply the muscles of the back. Cutaneous branches 

 are derived from each of these sets, the six upper ones coming 

 from the internal branches and the six lower ones from the 

 external branches. 



The ANTERIOR PRIMARY DIVISIONS, or intercostal nerves, are 

 twelve in number on each side ; each communicates with the 

 corresponding ganglion of the sympathetic chain. 



The UPPER six pass forwards in the intercostal spaces 

 below the vessels, lying at first between the pleura and 

 external intercostal muscle, then between the external and 

 internal intercostal muscles ; after giving off the lateral 

 cutaneous branches, they lie in the internal intercostal muscle, 

 and then between that muscle and pleura, extending forwards 

 to the sternum, and crossing the internal mammary artery, to 

 end as the anterior cutaneous nerves of the thorax by perforating 

 internal intercostal and pectoralis major. 



Branches : 



Lateral cutaneous : given off midway between head of rib 

 and sternum. .The ist intercostal nerve has generally no 

 lateral cutaneous branch. Each branch, except that from the 

 2nd nerve, then pierces the external intercostal muscle, and 

 divides into anterior and posterior branches, which supply 

 the muscles, mammary gland, and integument. 



The lateral cutaneous branch of the 2nd nerve, or intercosto- 



