(fl. Emesa [now Horns], Syria, A.D. 390–400)
Nemsius, possibly although not certainly a provincial governor of Cappadocia, is believed to have been converted to Christianity about 390, and sometime thereafter he became bishop of Emesa. During these final years of the fourth century he composed his treatise Πєρί ϕνσєως ᾶνθρὭПον (“On the Nature of Man”), which is essentially concerned with the reconciliation of Platonic doctrines on the soul with Christian philosophy and also, importantly, with the interpretation of Greek scientific knowledge of the human body from the standpoint of Christian doctrine. For a time the work was attributed to Gregory of Nyssa; and it was not until the seventh century that there was any ascription of it to Nemesius, of whom almost nothing is known except for such self-revelations as are to be found in his text. From these it is apparent that he was well-read in the writings of Galen and may even have had some medical training.
Although Nemesius’ book contains many passages dealing with Galenic anatomy and physiology, the most important contribution of the work was to establish the idea that the mental faculties were localized in the ventricles of the brain, a belief that was generally accepted and retained as late as the sixteenth century. Actually the belief in such localization had been advanced even earlier in the fourth century by the Greek physician Posidonius, to whom Nemesius referred; but because only fragments of Posidonius’ writings survived, the doctrine of ventricular localization gained prominence only through the later treatise.
According to Nemesius’ doctrine, all sensory perceptions were received in the anterior—now called lateral—ventricles of the brain. Later this area came to be designated the “sensus communis,” that is, the region where all the sensory perceptions were held in common by a force known as the faculty of imagination. The middle or, as it is now called, third ventricle was the region of the faculty of intellect, which controlled the “judging, approving, refuting, and assaying” of the sensory perceptions gathered in the lateral ventricles. The third faculty was that of memory, the storehouse of sensory perceptions after they had been judged by the faculty of intellect. Memory was located by Nemesius in the cerebellum but, according to succeeding interpretations, in the fourth ventricle. Moreover, later writers extended Nemesius’ doctrine by causing the intellectual or rational faculty to draw upon memory in the making of decisions. The faculties operated through the agency of the animal spirit, the very refined spirit which, according to Galen, was produced from vital spirit after it had been carried through the supposititious network of arteries, called the rete mirabile, at the base of the brain. Nemesius was convinced of the correctness of his doctrine of the ventricular localization of the mental faculties, since in his opinion injury to those areas of the brain caused the loss of the faculties.
After its composition Nemesius’ book seems to have gone through a period of disregard, to be rediscovered only after the passage of several centuries. It was cited by John of Damascus in the eighth century, by Timothy I, the Nestorian catholicos, and by the Phrygian monk and physician Meletius. Possibly it was from one of these sources that ventricular localization came to be accepted and described as early as the late ninth and early tenth centuries by Quṣtā ibn Lūqā and by al-Rāzī, the latter of whom was important in the diffusion of the doctrine.
The first extensive and medically important treatment of Nemesius’ book was that by Alphanus, a monk of the Benedictine abbey of Monte Cassino and later archbishop (1058–1085) of Salerno. Alphanus translated it into Latin under the title of Premnon physicon (“Tree of Nature”) and thus made the medical portions available to the Salernian medical school, although there is no clear evidence of their influence upon Salernian medicine. The work was again translated in 1155 by Burgundio of Pisa; neither translator appears to have been aware of the identity of the author. These Latin translations were definitely effective in promotion of the idea of the localization of the mental faculties in the ventricles—the former, for example, on Albertus Magnus and the latter on Thomas Aquinas. Localization began to be described with some frequency in the twelfth and thirteenth centuries. It was also illustrated by drawings of the head in which the lateral ventricles were often identified by circular figures, frequently called “cellulae” and specified as the area of “imaginatio,” “phantasia,” or “sensus communis”; a further circle representing the third ventricle was commonly designated as the area of “aestimativa” or “cogitativa,” and the circle of the fourth ventricle was most often labeled “memoria.”
The first translation of Nemesius’ work to be printed (Strasbourg, 1512) was that by John Cono of Nuremberg, and the first printed edition of the Greek text was published under the editorship of Nicasius Ellebodius by the Plantin Press of Antwerp in 1565.
The idea of ventricular localization of the mental faculties in the form presented by Nemesius was first attacked in 1521 by Berengario da Carpi, who grouped the three faculties in three separate areas of the lateral ventricles. Vesalius delivered the coup de grace to the entire theory in 1543, when he denied any role to the ventricles except the collection of fluid and declared that in some manner the mind was in the brain at large. Although Vesalius did not elaborate upon this point, his theme was picked up by Costanzo Varolio, who in 1573 asserted more clearly that there was a single mental faculty in the brain as a whole and that the ventricles served merely to collect and drain off superfluous fluid.
There is an English trans, of ΠєρίϕνσєωςᾶνθρὧПον by William Telfer in Cyril of Jerusalem and Nemesius of Emesa, W. Telfer, ed., vol. IV in Library of Christian Classics (London, 1955). It includes references to all the pertinent literature on Nemesius and eds. of his work.
C. D. O’Malley