THORACIC SPINAL NERVES. 501 



goes backwards between the transverse process of the corre- 

 sponding vertebrae, and, having got beneath the multifidus spirit, 

 is commonly subdivided into internal and external ramuscles. 

 The internal are the smaller, and are distributed upon the mus- 

 cles lying upon the spine, as the multifidus, the sacro-lumfralis, 

 longissimus dorsi, and so on: their terminating filaments reach 

 the skin. The external branches descend obliquely outwards 

 beneath the longissimus dorsi, and then issue between the latter 

 and the sacro-lumbalis, to both of which they dispense filaments: 

 they afterwards are divided into branches, which go to the tra- 

 pezius, latissimus dorsi, rhomboideus, and to the corresponding 

 integuments. 



The Anterior Branches of the Dorsal Nerves (Kami Sub- 

 costales) correspond with the intercostal spaces of the ribs. 

 Each one, in a short course after its origin, applies itself to the 

 rib just above it, and accompanies the intercostal vessels in the 

 groove, formed in the under margin of each rib. After it pro- 

 ceeds about two-thirds of the length of the rib, it separates gra- 

 dually from it, and goes nearer the middle of the intercostal 

 space and the superior margin of the rib below. To the angle 

 of the rib, each nerve is only covered in front by the pleura, 

 but afterwards it goes between the intercostal muscles. Near 

 the sternum, the branches become superficial by escaping from 

 between the intercostal 'muscles, and are distributed upon the 

 pectoral muscles, and the adjacent skin. These terminating 

 branches of the five or six inferior dorsal nerves go to the upper 

 portions of the abdominal muscles and their integuments. Not 

 far from its origin, each dorsal nerve anastomoses with the gan- 

 glion or cord of the sympathetic, after the manner described in 

 the account of the latter nerve.* 



There are some differences between the thoracic nerves in 

 their manner of distribution. 



* It is observed in pluritis, that there is a deposit of lymph, mixed with the 

 cellular adipose matter surrounding the sympathetic, its costal branches and the 

 subcostal nerves, until the latter get between the intercostal muscles. This in- 

 flamed state must, no doubt, produce particular nervous phenomena; as pain, 

 difficulty of respiration, and derangement of the functions of the abdominal 

 viscera. 



