396 SINUSES OF THE DURA MATER. 



of the cerebellum. Its convex border encloses the two 

 occipital sinuses. Its direction is vertical, extending from 

 the tentorium above, to the foramen magnum below. Other 

 reflections of the dura mater, called sphenoidal folds, are 

 seen on the sides of the sella turcica, forming the cavernous 

 sinuses. 



< Sinuses of the dura mater, (Fig. 112.) All the sinuses 

 are formed by reflections of the internal lamina of the dura 

 mater,, separating from the external, and leaving large 

 triangular cavities between them, lined with the same 

 membrane as that of the veins, all communicating with 

 each other, and designed for receiving the venous blood of 

 the brain. As many as fifteen sinuses are enumerated; 

 five of these being in pairs and five single. Those in pairs 

 are the two lateral, two superior petrosal, two inferior petro- 

 sal, two occipital, and two cavernous. The single are the 

 superior and inferior longitudinal, the straight, transverse 

 and circular. Others again make only eight, while Mr. 

 Tuson gives nine, which is the most commonly received 

 number. They are the following: 



1. Superior longitudinal sinus. 2. Inferior longitudinal 

 sinus. 3. Two lateral sinuses. 4. Vena magna Galeni. 

 5. The superior petrosal sinus. 6. Inferior petrosal sinus. 

 V. The two carvernous sinuses. 8. Circular sinus of Kid- 

 ley. 9. Torcular Herophili. 



In this, however, it will be seen there is no mention of 

 the occipital sinuses. The superior longitudinal sinus, as 

 just stated, describes the course of the superior margin of 

 the falx major ; when opened its form is seen to be trian- 

 gular, its base being above and its apex below, in the falx 

 little fibres called cordon- Willisii, are seen to cross it in 

 different places ; numerous orifices are seen throughout 

 the whole extent of this sinus, corresponding to the en- 

 trance of the veins from the cerebral hemispheres, dura- 

 mater, diploe, and pericranium. 



The glandular Pacchioni are seen connected with this 

 sinus in two positions, first on the outside of the dura mater 

 and near the sinus; and second within the sinus. They are 



