Since the opercular part of the inferior frontal gyrus (Area 44) is separated from the inferior tip of the precentral gyrus only by a shallow precentral sulcus, both of these 2 cortices form a continuous cortical area which is clearly separated from the superior temporal gyrus by the posterior ramus of the Sylvian fissure and also separated from the triangular part of the inferior frontal gyrus by the deep ascending ramus of Sylvian fissure. Another portion of the Broca’s area, triangular part of the inferior frontal gyrus corresponding to Area 45 is separated posteriorly by the ascending ramus and anteriorly by the horizontal ramus of the Sylvian fissure. Consequently, the two cortical areas consisting of the Broca’s area, opercular part and the triangular part of the inferior frontal gyrus, are horizontally disconnected from other adjacent cortical areas and connected only vertically with the rest of the brain areas. As a consequence, these two cortical areas are usually completely detached from the rest of the horizontal slice through Sylvian fissure.
Pierre Marie’s Error in Identifying the Cortical Areas
In his first paper [1], Pierre Marie showed a patient who did not show any language disturbance in spite of a destructive lesion of Broca’s area, but the destructive lesion of the case of this patient is actually situated anterior to the horizontal ramus of Sylvian fissure (Fig. 4a), that is to say on Area 46 of Brodmann and we can never know whether Broca’s area (Area 44 and 45) is affected or not, because these 2 cortical areas are completely missing from the illustration.
Fig. 4.a Marie’s non-aphasic case with a destructive lesion which Marie thought had destroyed Broca’s area but actually the lesion is located in Area 46. b Marie’s case with Broca aphasia without lesion on the Broca’s area. Areas 44 and 45 are missing. c Dejerine’s case cited by Marie as a case of Broca aphasia without lesion on the Broca’s area. Area 45 of the Broca’s area is evidently affected. (a cited from [1], Band c cited from [2]).
In his second paper [2], Marie showed an illustration of brain slice of Case Bal…, who clinically showed Broca’s aphasia (Fig. 4b). According to Marie, the lesions of this patient affected the “zone lenticulaire” and the deep white matter of the Wernicke area together with the white matter of the temporal lobe. But again, since both opercular and triangular parts of Broca’s area are missing from the illustration, we can never know whether these most important cortical areas are intact or not. In this paper [2], Marie cited the illustration of the brain slice of Bernheim’s case with Broca’s aphasia which appeared in Dejerine’s book (Fig. 4c). Marie discussed the clinicopathological similarities between these two cases, but the illustration of the Bernheim’s patient cited in Marie’s paper clearly shows that the opercular part of the inferior frontal gyrus corresponding to Area 44 is preserved but the triangular part of the same gyrus corresponding to Area 45 of the Broca’s area is totally damaged and atrophied. Marie seemed to have repeatedly made errors in identifying the anatomical site of the Broca’s area not only in his own cases, but also with the anatomo-pathological reports of other investigators [6].
Why Marie Did Not Notice the Missing Parts?
Then the question arises. Why Pierre Marie had repeatedly made this kind of simple error to identify the cortical areas? The answer is given by one of his last pupils form the United States. Percival Bailey, the famous neurosurgeon, entered Marie’s clinic at the Salpêtrière in 1921 as foreign assistant. He wrote “Only rarely did he enter the wards and never the laboratory, for he was very sensitive to formalin and would look at fixed brains only through a window, and there dictate his description” [7]. Although the above-mentioned anatomo-pathological studies of patients with aphasia were done in the Hospice de Bicêtre, and not in the Salpêtrière, he was sure to use it to observe the already cut horizontal brain slices indirectly through a window, as Bailey described. As shown in the previous Figures 1 and 4, two most important pieces of the posterior part of the inferior frontal gyrus, opercular and triangular parts are liable to be dropped out from the entire horizontal slice at the level of Sylvian fissure because they are not connected with the rest of the brain. My speculation is that Pierre Marie, in his routine laboratory works, made his assistants to cut the brains, but they did not pay enough attention to these 2 small pieces of brain inevitably detached from the rest of the brain slice.
Dejerine’s Error in Identifying Triangular Part
Similar error of identification of the easily detached small pieces of Broca’s area was also seen in Figure 225 of Dejerine’s “Anatomie de Centres Nerveux, Tome 1” [8]. The figure (Fig. 5) is a horizontal slice of normal brain and clearly shows two small pieces within the Sylvian fissure. Dejerine identified the posterior piece as Rolandic operculum and the anterior piece as frontal operculum, and the deep fissure between these two pieces as frontal opercular incisure, but the truth is that this deep fissure is ascending ramus of Sylvian fissure and the anterior piece which Dejerine identified as frontal operculum is actually the triangular part of the inferior frontal gyrus. Due to this misidentification of the ascending ramus of Sylvian fissure, Dejerine noted erroneously the above-mentioned anterior piece of brain as the opercular part and the cerebral gyrus situated anterior to this fissure as the triangular part (cap de la troisième circonvolution), but his anatomical identification was incorrect (Fig. 5).
Fig. 5. Dejerine’s error in identifying the triangular part of the inferior frontal gyrus (corrected anatomical names are given with arrows; modified from [8]).
Consequently, as to the identification of triangular part of the inferior frontal gyrus including Area 45 of Brodmann in the horizontal brain slice, Dejerine shared the same error with Marie. As shown above, Marie showed in his first paper [1] a case of his own who had no language impairment in spite of a lesion on the Broca’s area. The site of the lesion of this case was erroneously located on the triangular part by Marie, and the real site of the lesion was on the anterior part of the inferior frontal gyrus, probably Area 46 of Brodmann. Dejerine did not point out the misidentification of the site of the lesion of this case, since he had made the same error of identification of triangular part in the horizontal brain slice [8]. It seems rather very strange that both the experts in clinicopathological studies of aphasia had shared the same mistake. Marie’s papers finally elicited the famous aphasia debate in 1908, but the problem of