768 
gives the following observations on this 
subject. 
«© The importance of the sinuses in the 
circulation of the blood in the brain, is either 
vague described, or imperfectly understood 
by authors. We find it said, that the sinuses 
support the blood against coupression, and 
protect its free circulation. This to mie 
seems an erroneous idea. The lesser veins 
are as in other parts of the body, and have 
no such provision; and since, within the 
head, there can be no such partial compres- 
sion as in the limbs, any cause which would 
compress the greater veins, were they. not 
supported, must fall upon their extremities 
with worse effect. The circulation is the 
only power which can act mechanically upon 
the brain; but this can never cause a com- 
pression of its veins, because the increased 
action of the arteries must tend more to the 
distention of the veins than it will be the 
occasion of the brain compressing them. 
«« The more general idea conceived of the 
use of the sinuses is nearer the truth; viz. 
to prevent the sudden and violent action of 
the muscles of respiration, or of the muscles 
of the head and neck, from repelling the 
blood into the vena cava, or internal jugular 
veins; and consequently preventing the im- 
ulse from being communicated to the blood 
in the small and tender veins of the brain, 
which might endanger a rupture of them. 
Yet this is not exactly the manner in which 
the sinuses preserve the lesser veins { they 
do not suffocate nor take off the force of the 
impulse from the regurgitating blood, so 
much as they would do if they were like the 
trunks of veins in other parts; because, be- 
ing incapable of distention, they throw the 
undulation of the blood, when it is thus 
checked in its exit, backwards upon the ex- 
tremities of the veins. But then the effect 
is, that no particular vein or trunk receives 
the shock; all suffer in a lesser degree, and 
equally, which is their safety. All the veins 
in the base of the brain, which would be 
liable to rupture, or distention, from receiv- 
ing, in their sudden turns, the shock of the 
blood, checked by the muscles of respiration, 
or otherwise, are preserved by being inclosed 
in sinuses, and covered by the strong lamel- 
le of the dura mater. The lesser vessels 
again are removed from the shock : its force 
is spent, because it has spread among many 
branches ; and it has become a general im- 
pulse upon the brain, which the brain re- 
sists, because it is incompressible.” 
Monro’s explanation of the use of the 
sinusses, to which the author refers, in 
a note, is not given quite correctly. Dr. 
Monro does not say that the sinusses 
prevent the repulsion of blood, by the 
sudden action of the muscles of respira- 
tion into the vena cava and internal ju- 
gular, but that when the blood is so re- 
MEDICINE, SURGERY, ANATOMY, &e. 
pelled “ the impulse may not be com- 
municated to the blood in the small and 
tender veins of the brain, which would 
endanger a rupture of these,” and in 
confirmation of this opinion, he adds, 
that “ generally a very small quantity 
only of any liquor injected into the si- 
nusses enters the small veins of the brain 
and cerebellum.” 
The ventricles of the brain and origin 
of the nerves are described in the BL 
lowing chapter. Mr. Bell takes Willis’s 
arrangement of the nerves, allowing 
only nine of the encephalon ; whence the 
facial and auditory is included in the 
seventh pair, the glosso-pharyngeum, 
the vagum, and accessorium in the 
eighth, and the sub-occipital or tenth of 
Willis forms the first cervical pair, as 
Haller has proposed. 
We shall give a single specimen of the 
author’s talents for anatomical descrip- 
tion, that our readers may form some 
opinion of the execution of the work. 
Let us take part of the description of 
the par vagum, as being one of superior 
importance. 
«* The par vagum is the great and import- 
ant division of the eighth pair. It is the 
middle fasciculus of the three nerves as they 
lie within the seull. In its exit, it is sepa- 
rated from the internal jugular vein by a chin 
bony plate; and sometimes two or three 
fibres of the nerve pass the bone distinct from 
the others, and afterwards unite into the 
proper trunk of the par vagam. Deep under 
the lower jaw and the mastoid process, the 
glosso-pharyngeal nerve, the par vagum, the 
spinal accessory, the sympathetic nerve, 
the portio dura of the seventh, and the upper’ 
cervical nerves, are entangled in a way which 
will fatigue the dissector, and may account 
for every degree of sympathy of parts. The 
par vagum, lying behind the internal carotid 
artery, and as it were escaping from the con- 
fusion of the ninth accessory and glosso- 
pharyngeal nerves, descends and swells out 
into a kind of ganglion. We now observe 
three branches to be sent off: the first and 
second pharyngeal nerves, which pass to the- 
constrictor pharyngis muscle, and the in- 
ternal laryngeal nerve. This last mentioned 
nerve is even larger than the glosso-pha- 
ryngeal nerve. It is behind the carotid ar- 
tery, and passes obliquely downward and 
forward. In its progress the principal branch 
passes under the hyo-thyroideus muscle, and 
betwixt the os hyoides and the thyroid ear- 
tilage; while others, more superficial, pass 
down and are connected with the external 
laryngeal, or pharyngo-laryngeus; whieh is 
a nerve eant by the sympathetic, and par 
vagum conjointly. The principal branch of 
the internal laryngeal nerve, whieh runs 
