CHAPTER XIV. 



THE NERVOUS SYSTEM. 

 The Membranes and the Ventricles. 



THE DUE A MATER CEEEBEALIS. 



THE dura mater is a dense connective-tissue membrane which serves the double 

 purpose of a periosteum for the inner surface of the cranial bones, and of an investing 

 membrane for the brain. It is itself but poorly supplied with blood-vessels, but it con- 

 tains the large venous sinuses which carry the blood from the brain. Lesions of the 

 dura mater, therefore, are apt to be associated with lesions of the cranial bones, of the 

 pia mater, or of the venous sinuses. 



In young children the dura mater adheres closely to the inner surface of the cra-nial 

 bones, in adults it is more readily detached, and in old persons it is again more adher- 

 ent. Chronic inflammation of the external layers of the dura mater also renders it more 

 adherent to the bones. 



HAEMORRHAGE . 



Extravasated blood may lie between the dura mater and the cranial 

 bones, in the substance of the membrane, or between the dura mater and 

 the pia mater. 



Haemorrhages between the dura mater and the cranial bones are usu- 

 ally due to blows and injuries of the head, are of ten of considerable size, 

 separating the membrane from the bones, and may compress the brain. 

 They are often associated with laceration of the brain, and with haemor- 

 rhages between the dura mater and pia mater. 



Haemorrhages between the dura mater and the pia mater may take 

 place from the vessels of either membrane. Those from the vessels of 

 the dura may result from chronic pachymeniugitis. 



Haemorrhages into the substance of the dura mater are not frequent 

 and are usually small. 



Pressure on the head of the infant in delivery may cause extravasa- 

 tions of blood between the bones and the dura mater, as well as between 

 the bones and the pericranium. 



THROMBOSIS. 



Thrombosis of the venous sinuses is not uncommon. It is often associ- 

 ated with inflammation of the dura mater and with injuries and inflam- 

 mations of the brain and pia mater, of the cranial bones, of the middle 

 ear, and of the scalp. Like thrombosis in other parts of the body, it 



