A text-book of physiology for medical students and physicians . ther branches from the descending aorta. From the ana-tomical arrangement alone it is evident that the circulation in thebrain is very well protected from the possibility of being inter-rupted by the accidental closure of one or more of its arteries. Insome animals, the dog, one can ligate both internal carotids andboth vertebrals without causing unconsciousness or the death of theanimal. In an animal under these conditions a collateral circula-tion must be brought into play through the anastomoses of thespinal arteries. In man, o
A text-book of physiology for medical students and physicians . ther branches from the descending aorta. From the ana-tomical arrangement alone it is evident that the circulation in thebrain is very well protected from the possibility of being inter-rupted by the accidental closure of one or more of its arteries. Insome animals, the dog, one can ligate both internal carotids andboth vertebrals without causing unconsciousness or the death of theanimal. In an animal under these conditions a collateral circula-tion must be brought into play through the anastomoses of thespinal arteries. In man, on the contrary, it is stated that ligationof both carotids is dangerous or fatal. The Venous Supply.—The venous system of the brain is peculiar,especially in the matter of the venous sinuses. These large spacesare contained between folds of the dura mater or, on the base ofthe skull, between the dura mater and the bone. The channelhollowed out in the bone is covered with a roof of tough, inex-tensible dura mater, and indeed in some animals the basal sinuses. SjCulL. uusaTHatkr. Fig. 257.—Diagram to represent the relations of the meningeal membranes of the cere-brum, the position of the subarachnoidal space and of the venous sinuses. may in part be entirely incased in bone. The larger cerebral veinsopen into these sinuses; the openings have no valves, but, on thecontrary, are kept patent and protected from closure by the struc-ture of the dura mater around the orifice. The sinuses receiveblood also from the veins of the pia mater, dura mater, and fromthe bones of the skull through the diploic veins. The venous bloodemerges from the skull in man mainly through the opening of thelateral sinuses into the internal jugular vein, although there is alsoa communication in the orbit between the cavernous sinus and theophthalmic veins through which the cranial blood may pass intothe system of facial veins or vice versa, another communicationwith the venous plexu
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Keywords: ., bookautho, bookcentury1900, bookdecade1910, booksubjectphysiology
