THE ARACHNOIDEA. 561 
Pacchionian Bodies (granulationes arachnoidales)—When the surface of the 
dura mater is inspected after the removal of the calvaria, a number of small fleshy- 
looking excrescences, purplish-red in colour, are seen ranged in clusters on either 
side of the superior 
longitudinal sinus, Die aes 
and when this sinus Arachnoid mater 
is opened they are 
alsoobserved protrud- 
ing in considerable 
numbers into its in- 
terior. These are the 
Pacchionian — bodies, 
and they are also 
found in smaller 
numberand distinctly 
smaller size in con- 
nexion with other 
blood sinuses, such 
as the lateral sinus, 
the straight sinus, 
and the cavernous 
sinus. At first sight 
they appear to belong 
to the dura mater, but 
in reality they are 
projections from the 
arachnoidea. In the 
child they are exceed- 
ingly small and rudi- 
mentary, and it is 
only as life advances 
Phat theya become Fosterorprmary 74 
largeandconspicuous. 4 nterior primary 
Each Pacchionian division 
body Te bulbous Fic. 415.—MEMBRANES OF THE SPINAL CORD, AND THE RELATIONS THEY 
protrusion of the PRESENT TO THE SPINAL NERVE-Roots (A. M. Paterson). 
arachnoid membrane. 
It is attached to the arachnoidea by a narrow pedicle, and into its interior is pro- 
longed through this a continuation of the subarachnoid space and its characteristic 
—— Posterior nerve-root 
___Ligamentum 
denticulatum 
Anterior nerve-root 
Dura mater 
— Posterior nerve-root 
Anterior nerve-root 
Anterior nerve-root 
Ligamentum 
denticulatum 
Lateral column 
of cord 
———— Pia mater 
WS 
NE Posterior nerve-root 
N 
NX 
Spinal ganglion 
NG Posterior primary 
be 2 division 
Anterior primary division 
Anterior nerve-root 
Spinal cord 
meshwork. The Pacchionian bodies do not pierce the dura mater. As they push their 
way into a blood- 
sinus they carry 
before them a thin 
covering continuous 
Bone with the sinus wall. 
On either side of the 
Superior superior longitudinal 
ongitudinal Z 
sinus sinus there are a 
. number of irregular 
spaces in the dura 
mater which com- 
municate with the 
Fic. 416.—MESIAL SECTION THROUGH THE CRANIAL VAULT IN THE FRONTAL sinus either by a 
REGION. Displays the superior longitudinal sinus and the Pacchionian 
bodies protruding into it (enlarged). 
Pacchionian body Mouth of a vein 
small aperture or a 
narrow channel. 
These spaces are called the parasinoidal sinuses or the lacune laterales, and certain 
of the meningeal veins and some of the diploic veins open into them. Pacchionian 
bodies push themselves into the parasinoidal sinuses from below in such a manner 
that they receive a complete covering from the layer of dura mater which forms 
36 
