DURA MATER. 363 



The membranes of the encephalon are the dura mater, arachnoid 

 membrane, and pia mater. 



The Dura mater* is the firm, bluish, fibrous membrane, which is 

 exposed on the removal of the calvarium. It lines the anterior 

 of the skull and spinal column, and sends processes inwards 

 for the support and protection of the different parts of the 

 brain. It also sends processes externally, which form sheaths for 

 the nerves as they quit the skull and spinal column. ,Its external 

 surface is rough and fibrous, and corresponds with the internal table 

 of the skull. The internal 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 the pericardium and tunica albuginea of the testicle. 



On either side of the dura mater the branches of the middle me- 

 ningeal 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 ;f granular 

 bodies are also occasionally seen in its interior ; these are glandular 

 Pacchioni. 



The Glandulce Pacchioni^ are small, round, whitish granulations, 

 collected into clusters of variable size. They are found in three 

 situations. 1. On the inner surface of the dura mater near to the 

 superior longitudinal sinus ; when of large size they produce absorp- 

 tion of the dura mater, and considerable indentations on the inner 

 wall of the skull. 2. In the superior longitudinal sinus. 3. On the 

 arachnoid membrane investing the pia mater near to the margin of 

 the hemispheres. 



If the student cut through one side of the dura mater, along the 

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

 the middle line, he will observe the smooth internal surface of the 

 dura mater. He will perceive also the large cerebral veins filled 

 with dark blood, passing from behind forwards to open into the 

 superior longitudinal sinus, and the firm connexions, by means of 

 these veins and the Pacchionian bodies, between the opposed sur- 

 faces of the arachnoid membrane. 



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



* 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. 



\ These bodies have no analogy whatsoever with glands. Their nature and use are 

 but imperfectly known. They are not found in infancy. They are described as con- 

 globate glands by Pacchioni, in an epistolary dissertation. "De Glandulis conglobatis 

 Durae Meningis indeque ortis Lymphaticis ad Piam Matrem productis," published in 

 Romo, in 1705. 



