Abstract
Because of unilateral dominance (laterality) in speech function, the gyral configuration of the area related to this faculty discloses the morphologic differences between the left and right hemispheres to some degree. It is well known facts that the difference is distinct in the planum temporale and sensory speech area (of Wernicke). The motor speech area (of Broca) is considered to occupy the pars opercularis of the inferior frontal gyrus, almost coinciding with Brodmann's cytoarchitectonic area 44. From an angiographic point of view the posterior border of the pars opercularis can be defined by the precentral artery (PC=C in Figs. 1-4) as it passes through the inferior segment of the precentral sulcus. The anterior border of the pars is at the ascending ramus of the Sylvian fissure. Since the prefrontal artery (PF=B in Fig. 1-4) most frequently runs through this ramus, the artery indicates the anterior limit of the pars opercularis. Moreover, the artery can be properly identified on the anteroposterior view, when it runs through the anterior insular space and follows on deeper insular course than other arteries. The third landmark, the orbitofrontal artery (OF=A in Figs. 1-4) follows the horizontal ramus of the Sylvian fissure. On the anteroposterior view, this is likely deep in the fissure and lower in course than the prefrontal artery.
We studied both sides of the carotid angiogram in 48 persons without any gross morphologic lesion in the cerebra. Twenty-six subjects were male, and 22, female. Age ranged from 3-years-old through 66 years of age. Forty-six persons were right-handed, one left-handed and one ambidextrous.
We measured the distance from the midline the the innermost point of the precentral (C), prefrontal (B) and orbitofrontal (A) artery, respectively. The value of the measurement can be regarded as an inverse image of the depth of each sulcus or ramus of the fissure. That is to say, the deeper a sulcus was, the larger the cortical area established at its depth must be. These values were expressed as the percentage of the width of the ipsilateral hemisphere (Fog. 1-4, M). For all three measurement difference in the value between the left and the right was (Lt.-Rt.=) : +1.04% (for the precentral : C (PC/M)) : +2.2% (for the prefrontal : B (PF/M)) : and +1.37% (for the orbitofrontal : A (OF/M)) in 46 righthanded persons. In the one ambidextrous case, there was recognizable dominance of the right side.
One reason for this result is thoght to be that the difference in the motor speech area was not less distinct than that in the sensory speech area.
Another point of this investigation focused on the size of each artery and the difference between the right and the left. A larger artery has to have a larger irrigation area.Comparison of the caliber of corresponding arteries as described above suggests a certain difference between the left and right cortical area (Table 2). This comparison is of a practical value when evaluating the extent of the motor speech area in individual cases.
