The Marvelous Network and the History of Enquiry into Its Function

Greek and Roman physicians were fascinated by a structure lying just below the brain in certain mammals. They dubbed it the “rete mirabile,” or marvellous network, and believed it was present in humans, in whom it played an indispensable role, according to their opinion. Galen thought that it was the site of generation of animal spirit, the spirit of the very soul. Later physicians, however, recognized that the structure was absent in humans; but in those mammals that did possess it, its function remained unclear. This paper traces the history of this curious structure and its interpretation, concluding with an account of modern insight into its role in heat regulation.

The network lies in the floor of the skull just below the brain. It has twin parts, right and left, lying side by side. Fig. 1 depicts the right side (the side uppermost in the figure) as seen looking downward onto the floor of the skull of an ox, after removal of the brain. Its prominent wormlike convolutions have been exposed by the removal of a thin roof of bone that covered them, and are indicated by the arrow. They consist of intertwining small branches of the right internal carotid artery, just before that artery ends its upward journey through the floor of the skull; these branches then reunite and run upward into the skull cavity immediately below the brain. They supply their blood to the brain, initially as a single artery once more, which has been removed along with the brain in the view in Fig. 1. On the left side (i.e., just below, in Fig. 1) the corresponding convolutions are branches of the left carotid artery; they remain covered by their bony roof, and so they are not visible.

This rete was probably first identified and named “marvellous network” by associates of the anatomist Herophilus of Chalcedon, at Alexandria during the third century B.C.E. Galen, writing in the second century c.e., credits these anatomists with identifying the rete. ¹ It has also often been termed the “carotid rete.” Galen described it with enthusiasm and authentic detail:

It is not a simple network but [looks] as if you had taken several fisherman’s nets and superimposed them. It is characteristic of this net of Nature’s, however, that the meshes of one layer are always attached to those of another, and it is impossible to remove any one of them alone; for, one after another, the rest follow the one you are removing, because they are all attached to one another successively. ²

The authentic detail need not mean that the description was drawn from dissection of human cadavers. Galen’s own accounts of anatomy were drawn chiefly from dissection of apes, and he dissected other animals too. He had the advantage of having been physician to the gladiators of Pergamum for some two and a half years, acquiring an experience of their injuries, which his writings display. ³ But the site claimed for the rete is so deep within the head, and any injury there so instantly lethal, that gladiatorial experience could hardly prove instructive. Whether he ever dissected a human cadaver as a source of knowledge is a question long debated but impossible to resolve with certainty. Charles Singer (1876–1960), the London-based historian of medicine and science who translated a major work of Galen, remarked in 1956, toward the end of his life: “I have thought much on this topic and have several times changed my views, but now think that he had such knowledge.” ⁴ If Galen did ever see the relevant part of a human body, it can be argued that he was misled by the substantial venous plexus below the base of the brain in man and primates, which is not an arterial rete...