DURA MATER. 369 



The Glandula Pacchioni* are small, round, whitish granulations, oc- 

 curring singly or in clusters, and forming small groups of various size along 

 the margin of the longitudinal fissure of the cerebrum, and more particu- 

 larly near the summit of the latter. These bodies would seem to be of 

 morbid origin ; they are absent in infancy, increase in numbers in adult 

 life, and are abundant in the aged. They are generally associated with 

 opacity of the arachnoid around their bases, but in some instances are 

 wanting even in the adult. They have their point of attachment in the pia 

 mater, from which they seem to spring, carrying with them the arachnoid 

 membrane, and then, in proportion to their size, producing various effects 

 upon contiguous parts. For example, when small, they remain free or 

 constitute a bond of adhesion between the visceral and parietal layer of the 

 arachnoid ; when of larger size they produce absorption of the dura mater, 

 and as the degree of absorption is greater or less, they protrude through 

 that membrane, and form depressions on the inner surface of the cranium, 

 or simply render the dura mater thin and cribriform. Sometimes they 

 cause absorption of the wall of the longitudinal sinus, and projecting into 

 its cavity, give rise to the granulations described in connexion with that 

 channel. 



If the student cut through one side of the dura mater, in the direction 

 of his incision through the skull, and turn it upwards towards the middle 

 line, he will observe the smooth internal surface of this membrane. He 

 will perceive also the large veins of the hemispheres filled with dark blood, 

 and passing from behind forwards to open into the superior longitudinal 

 sinus ; and the firm connexion, by means of these veins and the Pacchi- 

 onian bodies, between the opposed surfaces of the arachnoid membrane. 

 If he separate these adhesions with his scalpel, he will see a vertical layer 

 of dura mater descending between the hemispheres ; and if he draw one 

 side of the brain a little outwards, he will be enabled to perceive the ex- 

 tent of the process of membrane, which is called the falx cerebri. 



The processes of dura mater which are sent inwards towards the interior 

 of the skull, are the falx cerebri, tentorium cerebelli, andjfafo cerebelli. 



The Falx cerebri (falx, a sickle), so named from its sickle-like appear- 

 ance, narrow in front, broad behind, and forming a sharp curved edge 

 below, is attached in front to the crista galli process of the ethmoid bone, 

 and behind to the tentorium cerebelli. 



The Tentorium cerebelli (tentorium, a tent) is a roof of dura mater, 

 thrown across the cerebellum and attached at each side to the margin of 

 the petrous portion of the temporal bone ; behind, to the transverse ridge 

 of the occipital bone, which lodges the lateral sinuses ; and to the clinoid 

 processes in front. It supports the posterior lobes of the cerebrum and 

 prevents their pressuref on the cerebellum, leaving only a small opening 

 anteriorly, for the transmission of the crura cerebri. 



The Falx cerebelli is a small process, generally double, attached to the 

 vertical ridge of the occipital bone beneath the lateral sinus, and to the 

 tentorium. It is received into the indentation between the two hemi- 

 spheres of the cerebellum. 



The layers of the dura mater separate in several situations, so as to form 



* These bodies are incorrectly described as conglobate glands by Pacchioni, in an 

 epistolatory dissertation, De Glandulis conglobatis Durse Meningis indeque ortis Lym- 

 pbaticis ad Piam Matrem productis," published at Rome, in 1705. 



f In leaping animals, as tl.e feline and canine genera, the tentormm forms a bony tent 



T 



