A. Cysts

Cysts properly belonging to the dura mater are extremely rare; though some examples have been met with in its substance of fat-cysts containing hair. I have in some cases seen tumors attached to the inner shining surface of the dura mater, which resembled lipoma; they were enclosed in a cellular sac, and more or less distinctly lobulated.

B. Fibroid Tissue

Besides the fibroid thickening of the dura mater which is found after inflammation, tumors of fibrous structure occur in that membrane. They are, however, very rare; in a great number of tumors I remember only some few which exhibited a genuine, developed, and undoubted fibrous structure. Very many growths in the dura mater have indeed an intermixture of fibres with their structure, differing in various cases in arrangement and degree, which gives them the appearance of a fibrous tumor. There is no doubt that the tumors on the petrous bone, particularly examined by Cruveilhier, were structures of this class supposed to be purely fibrous.

C. Productions Of Bone

What are called ossifications of the dura mater, are known to be very common. By these are generally meant the bony growths situated on the inner surface of the dura mater, especially of the falx. I do not, however, believe that these belong to the dura mater itself. From their analogy with similar formations on the cerebral, and especially on the spinal, arachnoid, as well as from special examination of their relations, I infer that they are connected with the arachnoid layer of the dura mater. They will be noticed more completely among the abnormal conditions of that membrane.

There are, however, some bony formations which undoubtedly belong to the dura mater. The osseous plates before alluded to, which become united to the cranial bones, and which are true bone, and the bony concretions sometimes developed in the dura mater, when it has become thickened and callous from inflammation, are of this kind.

D. Tubercle

Primary tuberculosis is as rare in the dura mater as it is in the fibrous system generally. The tubercles, which are often found adhering to the inner surface of the dura mater, are such as were originally developed in the peripheral cerebral substance, and subsequently came into connection with the dura mater by the formation of adhesions between them and the inner membranes. They do not belong, therefore, to the present section. On the other hand, the dura mater is not unfre-quently the seat of tubercular deposit and tubercular suppuration, when the cranial bones are carious from tubercular disease.