374 SPECIAL ANATOMY. 



moist surface is inseparably connected, by means of uniting tissue, 

 with the arachnoid. It is connected externally with the external 

 periosteum at tine foramina of the skull, through which the nerves 

 pass out, and forms prolongations internally which enter into the 

 fissures of the brain. These are : 



a. Falx cerebri, passing from the foramen ccecum and crista 

 galli, at first narrow, then broader, in the centre of the cranial 

 vault from before backwards, where its base falls vertically 

 upon the tentorium. The superior convex border reaches 

 from for. co3cum as far as protuberant, occipitalis, and con- 

 tains the sinus longitudinalis superior ; the inferior concave 

 touches the corp. callosum behind only, and contains a small 

 vein (sinus longitud. inferior) ; the lateral surfaces separate 

 the hemispheres of the cerebrum from one another. 



b. Tentorium cerebelli, a septum, placed transversely, is situ- 

 ated beneath the posterior lobes of the cerebrum and above 

 the cerebellum ; is maintained in mutual tension with thefafo 

 cerebri. The external larger circumference attaches behind 

 to the linece transvers., in front to the superior angle of the 

 petrous bone, and contains the sinus transversus. Its internal 

 smaller boundary is concave, and encircles the pons Varolii 

 and corpp. quadrigemina. The apices of the external cir- 

 cumference are attached to the proc. clinoid. posterr., those 

 of the internal to proc. clinoid. anteriorr., as they pass away 

 under the former (decussating), and bound the fossa pituitaria. 

 The sin. cavernosi are placed inside them. 



c. Falx cerebelli passes downwards from the protuberantia oc- 

 cipitalis interna, vertically, to the centre of the posterior 

 circumference of foramen magnum, where it divides into two 

 folds for the lateral parts of the foramen. The basis is in 

 contact with the tentorium ; the posterior border attaches it- 

 self to crista occipital, poster. The anterior looks towards 

 the base of the posterior fissure, the lateral surfaces towards 

 the inner surfaces of the posterior lobes of the cerebellum. 



Structure. The dura mater consists of two fibrous layers, 

 which in several places separate from one another, and form tri- 

 angular canals for the reception of veins : these are the sinus. 

 The fibres of the layers decussate in various directions. Between 

 the internal layer and that of the arachnoid, along the longitudinal 

 sinus, we find in the adult the white corpp. (glandul.) Pacchioni, 

 which often project into the sinus, and produce thinning of the 

 cranial bones. 



