THE SUPERIOR CAVAL SYSTEM. 



871 



When the latter veins are patent epistaxis may be a symptom of cerebral hyperaemia 

 (as in congestive headaches) and may relieve it. In children epistaxis, in infants 

 cedema of the scalp over the anterior fontanelle, and in adults oedema over the parie- 

 tal and occipital regions are common symptoms of thrombosis of this sinus, and are 

 easily understood in view of its venous tributaries. 



N^vi in the scalp in the mid-line sometimes communicate directly with the sinus 

 by veins passing between the parietals or directly through them near the medial edge. 



Traumatic or inflammatory thrombosis may follow a depressed fracture of the 

 cranial vault if the fragment invades the lumen of the sinus and obstructs or arrests 

 the flow of blood. 



A noninfective form of thrombosis is sometimes observed in connection with 

 this sinus. It has received the name of marasmic thrombosis, as it has usually been 

 associated with weakness and debility. 



The construction of all the sinuses predisposes them to thrombosis. Their 

 rigidity, their width, the trabeculae which occasionally cross them, the peculiar 

 manner in which they are prevented from being too rapidly depleted during inspira- 



FiG. 756. 



Crista galli 



Superficial Sylvian vein 



Superior longitudinal sinus 

 Right choroid vein 



Right vein of striate t)ody 

 Falx cerebri 

 Inferior longitudinal sinus 



Internal cerebral veins, uniting tc 

 form great cerebral (Galen's> 

 vein 



S:raight sinus 



Tentorium cerebellt (under 



surface, riglit half 



Right superior petrosal sinus 



Internal auditory meatus 



Torcular HerophiU 



Lateral superior cerebellar veins 



Right lateral sinus 



Falx cerebelU 



Right inferior petrosal sinus 



i^^^sB***''" 



Head has been sectioned to left of mid-sagittal plane and brain removed, showing dural septa in position; 

 terminal portions of some superior cerebral veins are seen upon the surface of falx cerebri. 



tion when the lowering of pressure takes place in the great cervical veins Cpage 878), 

 and, in the case of the longitudinal sinus, the direction in which the blood from the 

 cerebral veins enters at an obtuse or right angle against the current, all tend to retard 

 the flow of blood and favor coagulation. When to these conditions is added a 

 deficient supply of possibly defective blood, as in exhaustion or depletion from pro- 

 fuse diarrhoea, marasmic thrombosis is apt to occur (Macewen). 



The line of the sinus begins at the root of the nose and runs in the mid-line to 

 the external occipital protuberance. 



Rarely there are found in the mid-line of the vertex small reducible swellings to 

 which are feebly transmitted the brain pulsations. They are subpericranial, contain 

 venous blood, and connect with the longitudinal sinus through apertures in the skull, 

 either congenital, the result of bone disease or atrophy, or due to accident. 



3. The Inferior Longitudinal Sinus. — The inferior longitudinal sinus (sitjus 

 sagittalis inferior) (Fig. 756) is an unpaired sinus which lies in the inferior or free edge 

 of the falx cerebri. It begins at about the middle of the border of the falx and passes 



