722 
of the omo-hyoid muscle, in the substance of 
which it ramities. 
Plexus.—\mmediately below the tendon of 
the omo-hyoid, the descendens noni, uniting 
with branches given off by the second and 
third cervical nerves, forms a nervous arch, the 
convexity of which looks downwards and for- 
wards. This plexus lies under cover of the 
sterno-mastoid, and in front of the jugular 
vein. 
Sterno-hyoid and thyroid branches—From 
the convexity of the arch formed by this plexus 
two or sometimes more nerves proceed down- 
wards and inwards, and ramifying on the super- 
ficial surface of the sterno-hyoid and thyroid 
muscles, are distributed tothem. 
Cardiac branch.—Meckel states, that on the 
left side particularly he has been able to trace 
a branch from this plexus into the thorax along 
the pericardium as far as the heart. The cervi- 
calis descendens is observed sometimes to vary 
from the above description, in its course down 
the neck, and in its relation to the great vessels ; 
for, instead of lying anterior and external to 
the sheath, it is occasionally found to pass down 
within the sheath, and sometimes even behind 
it. Ihave also seen it pass for a short dis- 
tance within the sheath in the upper part of its 
course, becoming superficial about the centre 
of the neck, and then running down in ‘front 
of the sheath in the usual manner. 
These varieties in the course and relations of 
this nerve are not, however, very commonly 
met with. ' 
Thyro-hyoid branch.—The next branch given 
off by the ninth pair is where the nerve is 
sing under the tendon of the digastric, a 
ittle above the cornu of the os hyoides. Here 
it gives off a considerable branch named thyro- 
hyoid, from its distribution. This nerve passes 
from its origin downwards and inwards, cross- 
ing the lingual artery, to which it lies super- 
ficial, and is distributed to the thyro-hyoid 
muscle. 
From the origin of the thyro-hyoid branch 
the ninth nerve passes inwards between the 
hyoglossus and mylo-hyoid muscles, and at the 
anterior edge of the hyoglossus it plunges into 
the genio-hyoylossus, in the substance of which 
its terminating branches ramify. In this course 
the ninth nerve supplies filaments to the mylo- 
hyoid, the hyoglossus, the genio-hyoid, genio- 
hyoglossus, and lingualis. 
In the substance of the genio-hyoglossus the 
branches of the ninth nerve form distinct anas- 
tomoses with branches of the fifth (the gusta- 
tory); with this nerve the branches of the 
ninth form nervous loops or arches, the con- 
vexities of which look forwards, and from which 
branches pass off which may be traced to the 
mucous membrane of the tongue. There can 
be little doubt that these nerves are to be con- 
sidered as compound, containing filaments de- 
rived both from the ninth and fifth pair. Most 
anatomists state, that the ultimate branches of 
the ninth can be traced no further than the 
structure of the muscles which enter into the 
formation of the tongue, and this appears to be 
true with respect to the branches which do not 
NINTH PAIR OF NERVES. A 
anastomose with the fifth pair; but it is more 
than probable, although difficult to demon- 
strate, that from the anastomosis 
above, a nerve, com of filaments boll 
of the ninth and fifth, proceeds, and | 
distributed to the mucous membrane of th 
tongue. ; 
Comparative anatomy.—It has been t 
by Professor Mayer, that in the ox and som 
other Mammalia he has discovered a sma 
posterior root to the ninth nerve, having on 
a ganglion; to the investigation of this ha 
paid particular attention. I have repeatec 
and with care sought for this posterior root @ 
ganglion in the ox, and have never been 
to satisfy myself as to the existence of a 
posterior root to this nerve. = 
The anatomy, however, of this part in t 
is extremely interesting, and when exar 
may, perhaps, explain Mayer’s opinion, —__ 
In the dissections which I have made of 
ninth pair in the ox, the nerve was fou 
arise in the depression between the co 
olivare and pyramidale by several deli 
roots, in a manner very similar to what is 
served in the human subject; these roots 
formly formed two bundles, which perfo 
the dura mater separately, before doing w 
however, the most inferior of these two bu 
received a twig, which at first sight ap 
to be given off by the spinal accessor; 
/ 
os 
upon further and careful dissection, thi 
was found not to come from the spinal a 
sory, but to arise by a number of distinet 
from the side of the medulla spinalis, an 
to the roots of the spinal accessory, in ft 
and distinct from which it passed up int 
cranium, and joined the inferior of the 
bundles, which formed the origins of the 
and uniting with this passed out th 
anterior condyloid foramen. 
When this nerve was cleansed, the pi 
and coagulated blood removed, which ; 
loads these parts in the slaughtered ox, B 
largement or any thing resembling ag 
could be discovered on its course. This 
cannot be considered a posterior rool 
ninth pair, for its origin from the me 
anterior to that of the spinal accessory ; 
am inclined to think that this nerve in 
holds the same relation to the ninth 
spinal accessory does to the eighth. — 
be what Mayer supposes to be a poste 
to the ninth ? - 
Winslow speaks of a communica’ 
tween the spinal accessory and nin 
within the cranium, the existence of + 
the human subject is described by Se 
Meckel ;* I have never been able to 
such communication in man. 
On tracing the ninth nerve in the 
the anterior condyloid canal, it ¥ 
united into one trunk, and envelope 
strong neurilemma; nor could any 
be detected on the nerve in this part 
course. . 
In Birds, the ninth nerve is foun nt 
* See Manuel d’Anatomie, Meckel, v Li 
