406 DURA MATER, 



corresponding with the superior longitudinal sinus, and on either side 

 may be frequently observed some depressed fossae, corresponding with 

 the Pacchionian bodies. 



The membranes of the encephalon are the dura mater, arachnoid 

 memlirane, and pia mater. 



The DURA MATER* is the firm, whitish or greyish layer which is 

 brought into view when the calvarium is removed. It is a strong fi- 

 brous membrane, somewhat laminated in texture, and composed of 

 white fibrous tissue. Lining the interior of the cranium, it serves as 

 the internal periosteum of that cavity ; it is prolonged also into the 

 spinal column, under the name of theca vertebralis, but is not adherent 

 to the bones in that canal as in the cranium. From the internal sur- 

 face of the dura mater, processes are directed inwards for the support 

 and protection of parts of the brain ; while from its exterior, other pro- 

 cesses are prolonged outwards to form sheaths for the nerves as they 

 quit the skull and spinal column. Its external surface is rough and fi- 

 brous, and corresponds with the internal table of the skull. The in- 

 ternal surface is smooth, and lined by the thin varnish-like lamella of 

 the arachnoid membrane. The latter is a serous membrane. Hence 

 the dura mater becomes a fibro-serous membrane, being composed of 

 its own proper fibrous structure, and the serous layer derived from the 

 arachnoid. There are two other instances of fibro-serous membrane in 

 the body, formed in the same way, namely, the pericardium and tu- 

 nica albuginea of the testicle. 



On the external surface of the dura mater the branches of the mid- 

 dle meningeal artery may be seen ramifying ; and in the middle line is 

 a depressed groove, formed by the subsidence of the upper wall of the 

 superior longitudinal sinus. If the sinus be opened along its course, 

 it will be found to be a triangular channel, crossed at its lower angle 

 by numerous white bands, called chordae Willisii+; granular bodies 

 are also occasionally seen in its interior, these are glandulae Pacchioni. 



The Glandules Pacchioni^. are small, round, whitish granulations, 

 occurring singly or in clusters, and forming small groups of various 

 size along the margin of the longitudinal fissure of the hemispheres, 

 but more particularly on the middle of this border. These bodies 

 would seem to be of morbid origin ; they are absent in infancy, in- 

 crease 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 



* So named from a supposition that it was the source of all the fibrous 

 membranes of the body. 



t Willis lived in the seventeenth century ; he was a great defender of the 

 opinions of Harvey. 



J These bodies are incorrectly described as conglobate glands by Pacchioni, 

 in an epistolary dissertation, '" De Glandulis conglobatis Durse Meningis 

 indeque ortis Lymphaticis ad Piam Matrem productis," published in Rome, in 

 1/05. 



