THE NERVES. 411 



surfaces of the first and second, and those of the second 



and third fingers. 



b. Ram. profundus s. muscularis, passes through or under m. 

 supinator brevis upon the dorsal surface of the fore-arm, sup- 

 plies the extensor muscles, and passes close upon the lig. in- 

 terosseum (as n. interossens externus), to terminate upon the 

 carpal articulation. 



661. II. The Nerves of the Back, Nervi dorsaks (twelve pairs). 



The first passes out between the first and second dorsal, the last 

 between the twelfth dorsal and first lumbar vertebra. Their roots 

 are smaller, and lie more widely asunder than those of the other 

 spinal nerves ; their trunks also are less developed. They traverse 

 a greater length of the canal, spinalis, form their ganglia, and soon 

 divide after their exit from the intervertebral foramen. By means 

 of frequent anastomoses, they form arched loops with each other, 

 and give off roots to the nerv. sympathicus. 



1. Posterior branches, rami dorsales, smaller than the anterior, 

 turn round between lig. colli costce extern, and intern. , backwards, 

 and divide into an external and internal branch. 



a. Rami externi, turn outwards : 



a. Those of the seven superior, smaller, pass out between the 

 transverse processes ; pass between m. longissim. and sa- 

 cro-lumbalis, give branches to them, to cervical, descend. 

 and transversal., to levatores costarum, and the over-lying 

 skin. 



/3. Those of the five inferior are larger, perforate the tendons 

 ofserratus posticus and latissimus dorsi, and terminate 

 below in the skin. 



b. Rami interni, are larger in the seven superior dorsal nerves; 

 pass upon m. multifid. spines, inwards and downwards to- 

 wards the transverse processes, give branches to m. mutifid., 

 semi-spinal, cervicis and dorsi, mm. inter spindles, perforate 

 the superficial muscles, and spread out, as the two are asso- 

 ciated together, externally in the skin of the back. 



2. The anterior branches, nervi intercostales, pass between the 

 ribs before the lig. colli costce intern., traverse, below the vasa in- 



fracostalis, the sulcus costalis, between mm. intercostales externi 

 and interni, forwards and outwards, and divide in the middle be- 

 tween vertebrce and sternum into an internal and external branch. 

 The anterior branch of the first dorsal nerve assists in forming the 

 plex. brachialis, as its superior branch passes upwards behind art. 



