632 



NERVOUS SYSTEM. (NERVOUS CENTRES. THE MENINGES.) 



dinal sinus above; one for the straight sinus in 

 front ; two for the lateral sinuses on each side ; 

 and two for the occipital sinuses inferiorly 

 (Jig. 362, 0- 



Posterior part of the cranium removed, to shew the 

 dura mater and the superior longitudinal, and the 

 lateral sinuses, ivith the torcular Herophili. 



e, lateral sinus ; t, torcular Herophili ; s, superior 

 longitudinal sinus. 



Lateral sinuses. From each side of the con- 

 flux of the sinuses, there proceeds in a some- 

 what serpentine course outwards, downwards, 

 and forwards, a wide canal, the largest of the 

 sinuses, which conveys the blood from the 

 torcular to the internal jugular vein. A groove 

 exists on each side of the internal occipital pro- 

 tuberance, for the reception of this sinus, which 

 marks the occipital bone, the mastoid portion 

 of the temporal, and a small portion of the 

 occipital bone again. In a great portion of 

 their course, the lateral sinuses correspond to 

 the posterior margin of the tentorium cerebelli, 

 as far forwards as the mastoid portion of the tem- 

 poral bone. Here each sinus winds downwards 

 to reach the jugular foramen in the posterior 

 lacerated opening. These sinuses are never 

 equal ; that of the right side being, with few 

 exceptions, the larger, a circumstance which 

 Vicq d'Azyr, Soemmering, and Kudolphi attri- 

 buted to the fact that most persons sleep on the 

 right side, on which account the blood is apt 

 to accumulate to that side. They are more 

 capacious at their termination in the jugular 

 veins than at their commencement from the 

 torcular. The inner surface of this sinus is like 

 that of all the others ; it is not, however, tra- 

 versed by any of the bands which are found so 

 numerous in the longitudinal sinus. Cruveil- 

 hier states that he once saw in the horizontal 

 portion of this sinus, a few of the Pacchionian 

 bodies. 



In its course each lateral sinus receives veins 



from the inferior surface of the brain and supe- 

 rior of the cerebellum; it also receives the supe- 

 rior petrosal sinus near the base of the petrous 

 portion of the temporal bone. A large mastoid 

 vein communicates with this sinus and pene- 

 trates to the exterior, where it forms one of the 

 principal sources of the occipital vein, thus 

 establishing a free and direct communication 

 between the circulation within and that with- 

 out the cranium.* Near the jugular foramen 

 the lateral sinus receives the inferior petrosal. 



None of the sinuses has been more fre- 

 quently the seat of inflammatory disease than 

 the lateral. Being the principal channel for 

 the return of the venous blood from the in- 

 terior of the skull, a slight morbid action within 

 them can scarcely fail to induce a material de- 

 rangement of the cerebral circulation, and the 

 nearness of their position to the cerebellum and 

 to the posterior lobes of the brain renders it 

 very unlikely that those parts would escape 

 participating in any acute disease which might 

 arise withm it. 



Occipital sinuses. These are small veins 

 lodged between the layers of the falx cerebelli. 

 They collect the blood from the dura mater and 

 from the cranial bones in the immediate vici- 

 nity of the posterior margin of the foramen 

 magnum, and from thence they pass upwards 

 and inwards to open into the lower part of the 

 torcular. Cruveilhier suggests that the direc- 

 tion and position of the occipital sinuses are 

 best indicated by describing them as being the 

 cords of the arcs which the lateral sinuses 

 form. 



Petrosnl sinuses. These sinuses are so 

 named from their connection with the petrous 

 portion of the temporal bone. The superior 

 petrosal sinus corresponds, on each side, to the 

 posterior superior edge of the petrous bone, 

 along the three outer fourths of which a groove 

 exists for its reception. This groove is inter- 

 rupted in front by a depression in which the 

 fifth nerve is lodged, so that at this place that 

 nerve lies between the sinus and the bone. The 

 superior petrosal sinus is about large enough to 

 contain an ordinary sized surgeon's probe. It 

 communicates with the lateral sinus posteriorly 

 and with the cavernous sinus in front, and in 

 its course it receives several small veins from 

 the dura mater in the middle fossa of the cra- 

 nium. It receives a vein from the anterior por- 

 tion of the corresponding hemisphere of the 

 cerebellum, and also, sometimes, one from the 

 inferior surface of the brain. Small veins from 

 the pons Varolii empty themselves into its an- 

 terior extremity. 



The inferior petrosal sinuses also form an 

 additional channel of communication between 

 the lateral and cavernous sinuses. They are 

 larger but shorter than the superior. In situ- 

 ation they correspond to the interval between 

 the petrous bone and the occipital. They open 

 into the inferior portion of the lateral sinus just 

 before it unites with the jugular vein. 



Transverse sinus. This sinus establishes 

 a communication between the petrosal and 



* Cruveilhier, An. Dcsc. t. iii. p. 268. 



