In the temporal lobe Mills locates four other centers which include the pole, the inferior temporal gyrus and a part of the middle temporal gyrus (Fig. 76). These are from before back ward: the center of intonation at the pole, the naming center, the center of equilibration, and the center of orientation.
The naming center Mills locates in the inferior temporal gyrus, just anterior to the middle of the infero-lateral border of the hemisphere. I have studied a case of Dr. Gamble's in which a pistol wound of this region was followed by entire loss of ability to name familiar objects.
All the above motor, somwsthetic and special sense areas are provided with projection fibers which connect them with defi nite muscle groups and surface regions and with the organs of special sense. Large parts of the cerebral cortex possess no pro jection fibers; they are believed to be associative in function.
Association Centers of Flechsig.—Flechsig describes three association centers, the anterior, middle, and posterior. Ante rior Association Center (Fig. 78).—According to Flechsig, that part of the frontal cortex which embraces region 35 of Flechsig and is anterior to the psychic motor region determines the temperament and individuality of the person; and as Mills declares, is the center of inhibition, self control, attention, con centration, volition. It is the center of "the abstract concept" (Fig. 76). J. S. Bolton says of this association center that "it is the last part of the cerebrum to be developed, and is the first to undergo dissolution; it is under-developed in amentia of all grades and atrophied in dementia, according to its degree." "It possesses the highest (mental) function" (Brain, Vol. 29). The posterior association center is composed of those portions of cortex situated between the sensory region of the equatorial zone in front and the visual cortex of the occipital lobe behind and embraces several intermediate regions of Flechsig and No. 34 of the final regions. This is an association center of the senses (Fig. 74). To acquire knowledge of the external world is thus the function of the posterior association center. Mills calls it the center of "the concrete concept" (Fig. 76). It includes there psychic areas, the common sensory, auditory and visual. Flechsig regards the island (of Reil) and the greater part of the middle and inferior temporal gyri, all except the anterior ends, including the final regions Nos. 32 and 36 of Flechsig, as the middle association center (Figs. 78 and 79). Lesions in it are followed by paraphasia, loss of ability to name objects, etc.
Destructive lesions of parts of the motor or sensory cortex cause merely loss of certain motions and sensations represented by those parts, but ablation of association centers disconnects the sensory, the psychic and the motor regions and causes aphasia, agraphia, change of temperament, impairment of the so-called moral and intellectual faculties, etc. Ablation of the visual
psychic center or auditory psychic center produces mind-blind ness in the former and in the latter mind-deafness.
Cell and Fiber Lamination of the Cerebral Cortex.—There is a type of cerebral cortex which, with small but definite varia tions, prevails throughout the cerebrum, excepting in the visual and olfactory regions (Fig. 8o). Though Dr. Campbell's divi sion of the cortex into seven layers of cells is complicated, it is similar to Cajal's description and I think it entirely worthy of general adoption and shall follow it in this work. It is to be regretted that the fiber and the cell layers have not been more satisfactorily correlated, as this would assist in detemining function. Dr. Alfred W. Campbell gives the layers as follows: First, the layer of cells: i. The plexiform or molecular layer.
2. The layer of small pyramids.
3. The layer of medium-sized pyramids.
4. The external layer of large pyramids.
5. The layer of stellate or polymorphous cells.
6. The internal layer of large pyramids.
7. The layer of fusiform cells.
Second, the fiber zones: i. The fiberless layer, or neuroglia zone.
2. The zonal layer, stratum zonale.
3. The supraradiary zone.
4. The Baillargic zone, outer and inner line of Baillarger.
5. The radiary zone.
6. The felt-work of Kaes.
T. The plexiform layer has next the surface a fiberless zone of neuroglia, on account of which it is often called the neuroglia layer. Underneath the neuroglia is a more or less dense plexus of nerve fibers, constituting the stratum zonale; and then an area of sparsely scattered fibers that belongs to the supraradiary zone. Scattered here and there in the zonal and supraradiary regions of the plexiform layer are small stellate cell-bodies, four or six microns in diameter, belonging to the types of Golgi and Cajal, whose dendrites and axones ramify in the stratum zonale, some near the cell-body and others at a considerable distance from it. There are also some large horizontal cells whose axones run tangentially within the stratum zonale. The stratum zonale also contains dendritic processes from subjacent laminw, the T-branched axones of Martinotti's cells, and, perhaps, the end-tufts of incoming fibers from the commissural, the associa tive and the projection systems. It is very well marked in the motor area (Fig. Si), not so well in the common sensory area (Fig. 82.) In the uncus it is very distinct (Fig. 84) and is so thick and dense in the gyrus hippocampi (the subiculum) as to be visible to the naked eye (Fig. 85). The zonal layer of fibers is faint in the visuo-sensory and audito-sensory cortex. The stratum zonale appears to grow richer with the education of the individual. The function of the plexiform layer is commonly thought to be association.