402 SPECIAL ANATOMY. 



branches to m. omo-hyoidem [and a long filament for the 

 posterior belly], sterno-, hyo-, and thyreoideus, and passes 

 behind the last to the plex. cardiac, super., and with another 

 branch to the nerv. pkrenicus in the mediastin. anticum. 

 Nerv. hypoglossus is a motor nerve only. 



649. The Spinal Nerves, Nervi spindles. 



From thirty-one to thirty-two pairs are enumerated, namely : 

 eight cervical, twelve dorsal, five lumbar, five sacral, and one to 

 two coccygeal pairs of nerves. 



They arise with two roots from the sides of the anterior and 

 posterior columns of the medulla spinalis, connected with the 

 gray matter in the interior. 



The anterior (motor) root is smaller than the posterior, separated 

 from it by means of the ligam. denticulatum, and arises from a 

 narrow white line. The posterior (sensitive) root is stronger, 

 arises from the gray lateral sulcus, and is provided with a gan- 

 glion (ganglion spinale). 



Course. Both roots, enveloped in arachnoid, approach each 

 other, without anastomosing, and pass out, even still surrounded 

 by a sheath of the dura mater, through a corresponding inter ver- 

 tebral foramen. The superior spinal nerves pass off horizontally, 

 and are shorter, the inferior at so much the more of an acute 

 angle with the spinal cord, the nearer they approach its termina- 

 tion. The two roots unite into one trunk after their exit from the 

 intervertebral foramen, which immediately divides into an anterior 

 and posterior, and branches for the n. sympathicus. Fibres from 

 the anterior as well as from posterior roots are united in these 

 branches. 



a. Ganglia spinalia, reddish, firm ganglia, formed by the pos- 

 terior roots of the spinal nerves, are situated one in each interver- 

 tebral foramen ; but those of the sacral and coccygeal nerves, 

 while still within the canalis spinalis and the dura mater. They 

 are so much the larger, the stronger their roots and the branches 

 passing off. The anterior roots of the spinal nerves are merely 

 applied to their anterior surfaces (according to Cruveilhier they 

 are also united to them by fibres). 



b. The anterior branches of the spinal nerves are, with the 

 exception of the first and second cervical, much stronger than the 

 posterior, flat, and pass forwards and outwards before the trans- 

 verse processes. In the neck, the loins, and sacrum, they form 

 loops by means of ascending and descending branches, in conse- 

 quence of which a plexus arises, from which the nerves pass off 



