THE DEEP CONNEXIONS OF THE CRANIAL NERVES. 477 
pervaded by an intricate network of fine fibrils. In form it is elongated and 
_ rod-like, and in length it is somewhere about 18 mm. It extends from a point 
- immediately above the decussation of the pyramids up to the level of the strive 
acustice. The lower portion of the nucleus is thus placed in the closed part of the 
medulla (Fig. 340, p. 457), whilst its upper part is situated in the open part of the 
medulla (Fig. 343, p. 460). The former lies in that part of the central gray matter 
which is continuous with the basal part of the ventral horn of gray matter of the 
cord. It is thus placed on the ventral and lateral aspect of the central canal, 
close to the mesial plane and the corresponding nucleus of the opposite side. The 
upper part of the nucleus occupies a position in the gray matter on the floor of 
the fourth ventricle, subjacent to the surface area, which has been described under 
the name of the trigonum hypoglossi. Within the nucleus the axons of the cells 
arrange themselves in converging bundles of fine fibrils, which come together and 
leave the ventral aspect of the nucleus as the fasciculi of the nerve. The nerve 
bundles thus formed traverse the entire antero-posterior thickness of the medulla 
between the formatio reticularis grisea and the formatio reticularis alba, and 
emerge on the surface in linear order at the bottom of the furrow between the 
olivary eminence and the pyramid. In the substance of the medulla, the root- 
bundles of the hypoglossal pass between the main inferior olivary nucleus and the 
mesial accessory olivary nucleus, and many of them on their way to the surface 
pierce the ventral lamina of the main olivary nucleus. 
> No decussation between the nerves of opposite sides takes place in the medulla, 
but commissural fibres pass between the two nuclei (Kolliker). Further, numerous fibres 
from the opposite pyramidal tract enter the nucleus and end in connexion with its cells. 
The nucleus is thus brought into connexion with the motor area of the opposite side of 
the cerebral cortex. 
Spinal Accessory Nerve (nervus accessorius).—The spinal accessory is likewise 
a motor nerve, and it is generally described as consisting of a spinal and a 
medullary or accessory part. 
The spinal part of the nerve emerges by a series of roots, which issue from the 
surface of the lateral column of the upper part of the cord as low down as the fifth 
cervical nerve. These take origin in a column of cells situated in the anterior horn 
of gray matter of the cord close to its lateral margin, and immediately behind the 
Column of Goll Column of Burdach 
Entering 
posterior nerve 
root 
if . 
wus 
POST. 8OCT» 
a 
lee cng 
Nae = 
Substantia 
gelatinosa 
Rolandi 
CENTRAL 
) 
CANAL dl Emerging 
fascicle of spinal 
accessory nerve 
Fibres of origin 
of spinal 
accessory 
Emerging 
APT. KOCK 
root 
| Fic. 854.— DIAGRAM OF THE SPINAL 
ORIGIN OF THE SPINAL ACCESSORY 
NERVE (after Bruce). 
( ) Fic. 355.—SEcTION THROUGH THE UPPER PART OF THE 
CERVICAL REGION OF THE CorD (Orang), 
Showing the origin of the spinal part of the spinal accessory 
nerve, 
nerve-cells which give rise to the fibres of the anterior roots of the upper five 
cervical nerves. The cells of the accessory nucleus are large, multipolar, and in 
every respect similar to the motor cells of the spinal nerves. The axons from these 
