THE SINUSES OF THE CRANIUM. 52 1 



Varieties. The veins of the cerebrum are very variable in their arrangement, a condition 

 which may be explained by the number and size of their communications. The middle 

 cerebral rein may open into the spheno-parietal or superior petrosal sinus, or into the 

 beginning 1 of the basilar vein. The veins of Galen often terminate independently in the 

 straight sinus, without uniting into a " vena magna." In one instance they ascended, one on 

 the inner surface of each cerebral hemisphere, to the superior longitudinal sinus (Testut) 

 The anterior cerebral rein is sometimes wanting. The basilar vein may enter the vena magna 

 Galeni or the straight sinus. 



(Trolard, " Recherches sur 1'anatomie du systcme veineux de 1'encephale et du crane," These, 

 1868, and in Arch. gen. de He'd., 1870; C. Labbe, "Note sur la circulation veineuse du 

 cerveau," &c., Arch, de Physiol., 1879; J. Symington, "On the Valvular Arrangements in 

 connection with the Cranial Venous Circulation," Brit. Med. Journ., 1882; Browning, "The 

 Veins of the Brain and its Envelopes," Brooklyn, 1884 ; Gr. Sperino, " Circolazione venosa del 

 capo," Torino, 1884 ; E. Hedon," Etude anatomique sur la circulation veineuse de I'enc6phale." 

 These, 1888, and in Internat. Monatschr. f. Anat., 1889.) 



VENOUS SINUSES OF THE CRANIUM. 



The sinuses are channels contained within the substance of the dura mater, and 

 lined by a delicate membrane which is continuous with the internal coat of the 

 veins. They admit of a division into two groups, viz., a supero-posterior group, 

 lodged almost entirely in the processes of the dura mater, and an infero-anterior 

 group, situated in the base of the skull. To the former belong the superior longi- 

 tudinal, the inferior longitudinal, the straight, the lateral, and the occipital sinuses : 

 the latter includes the cavernous, the circular, the superior and inferior petrosal, 

 and the basilar sinuses. 



The superior longitudinal sinus (fig. 402, 1) commences at the crista galli, 

 where it sometimes (constantly in the child) has a communication with the veins of 

 the nasal cavity through the foramen caecum, and extends backwards in the upper 

 border of the falx cerebri, occupying the median groove on the inner surface of the 

 calvaria, and increasing gradually in size as it proceeds. In form it is three-sided, 

 and its cavity is bridged across by several fibrous bands, the chorda Willisii. Con- 

 nected with the sinus on each side is a series of irregular cavities in the dura mater, 

 the lacunae latemles of Key and Retzius, into which the Pacchionian bodies of the 

 arachnoid project from below, while their thin upper wall lines the corresponding 

 depressions of the calvaria. Internally they are continued into the sinus by com- 

 paratively narrow apertures or canals, and externally each usually receives a branch 

 of the meningeal veins. They vary in number and size, and increase in extent 

 with advancing years : the largest are found in the region of the vertex, where they 

 may be more than an inch in length. The sinus receives the superior cerebral 

 veins, which often communicate with the lacunae as they traverse the dura mater. 

 It also communicates in many cases with the veins of the scalp, by means of an 

 emissary vein which passes through the parietal foramen. As it descends on the 

 occipital bone the superior longitudinal sinus usually deviates a little from the 

 middle line, and inclines to one side (more frequently the right) of the internal 

 occipital protuberance, where it becomes somewhat enlarged and bends sharply 

 round at a right angle to be continued into the corresponding lateral sinus. This 

 dilatation is lodged in a well-marked depression on the occipital bone, and constitutes 

 what is termed the torcular fferophiH or the confluence of the sinuses. From it a 

 cross branch of variable size proceeds over the front of the occipital protuberance to 

 a similar bend formed by the straight sinus passing into the lateral sinus of the 

 opposite side. 



The inferior longitudinal sinus (fig. 402, 2) is very small, and has so much of 

 a cylindrical form that it is sometimes named inferior longitudinal vein. It passes 

 backwards in the posterior half or more of the lower border of the falx cerebri, and 



