1888 ] 95 [Stowell. 
D&scCRIPTION. 
Ectal Origin and Entocranial Course.—The N. accessorius is peculiar 
in its two-fold origin, the medulla and the myel; the cephalic roots arise 
in the’ depression line dorsad of the area ovalis and immediately cau- 
dad of the dorsal roots of the N. vagus; the caudal roots arise along the 
lateral column of the cervical myel, as far caudad as the fifth cervical 
vertebra (fibres are not infrequently traceable along the entire cervical 
myel). The confluence of these funiculi forms a nerve trunk whose 
volume increases from its caudal origin to the foramen of exit. The nerve 
trunk thus constituted lies entad of the myelic dura opposed to the lateral 
column of the myel, between the dorsal and the ventral roots of the 
myelic nerves ; its course is cephalad and enters the cranium through the 
foramen magnum ; at the caudal border of the ectal roots of the N. vagus, 
the N. accessorius turns laterad and perforates the dura just caudad of the 
Vagus (I have not met with two entocranial trunks, as is sometimes the 
case in man), and takes its exit from the cranium through the foramen 
jugulare in the common sheath with the Vagus and the adjacent Glosso- 
pharyngeus. 
Just centrad of the foramen of exit the Accessorius is closely opposed 
to the G. jugulare (Vagus), to which ganglion it gives a large ramus. This 
is the so-called accessory or motor root of the N. vagus. 
Intercranial Relations and Foramen of Bxit.—The N. accessorius tra- 
verses the jugular fossa, in which it lies caudad and laterad of the N. 
vagus, but apparently in a common sheath with that nerve (additional 
histological research may disclose a separate sheath for each nerve), and 
leaves the cranium by the foramen jugulare. : 
Hctocranial Trunk.—The first 5-10 mm. of the ectocranial trunk are 
involved in the dense plexus, Pl. gangliformis or Pl. nodosus (Fig. Plex- 
us), with the Vagus. This plexus is formed by interlacing fibres of the 
Vagus, the Accessorius, a few fibres from the Hypoglossus, with nume- 
rous embracing and intertwining filaments of the N. sympathicus, and the 
vessels of this region; it is highly probable that the adjacent N. glosso- 
pharyngeus with its G. petrosum is involved in this plexus. 
Peripherad of the plexus, the N. accessorius lies entad of the A. occipit- 
alis and the V. jugularis (a ramule of the A. occipitalis is dorsi-laterad of 
the nerve in its ecto-cranial course as far as the A. occipitalis). At the 
caudal border of the A. occipitalis, the Accessorius bends dorsi-caudad, 
accompanied by a small arteriole and perforates the M. clavo-mastoideus 
near its dorsal border, 20-25 mm. caudad of the insertion of the muscle ; 
this point is also dorsad of the cephalic end of the thyroid body. 
PrincreaL Rami. 
N. clavo-mastoideus.—As the Accessorius perforates the M. clavo- 
mastoideus a large ramus (Fig. Clv.-Mas. ca.) is given to that muscle ; it 
is accompanied by an arteriole, lies upon the ental surface of the muscle, 
