An American text-book of physiology . shown in the accompanyingtable, found in man increasing numbers of large nerve-cells in the ventralhorns of the spinal cord at the ages named : Number of Developed Cells in the Cervical Enlargement of Man aiDifferent Ages (Kaiser). Age. Number of Nerve-cells. Fetus, 16 weeks 50,500 32 118,330 New-born child 104,270 Boy, fifteen years 211,800 Male, adult 221,200 Schiller: Compter rendus de PAcademic dcs Sciences, Paris, 1889.* Die Functionen der Gangliemellen des Halsmarkes, Haag, 1891. CENTRAL NERVOUS SYSTEM. 729 Here, as in the frog, the apparent increase
An American text-book of physiology . shown in the accompanyingtable, found in man increasing numbers of large nerve-cells in the ventralhorns of the spinal cord at the ages named : Number of Developed Cells in the Cervical Enlargement of Man aiDifferent Ages (Kaiser). Age. Number of Nerve-cells. Fetus, 16 weeks 50,500 32 118,330 New-born child 104,270 Boy, fifteen years 211,800 Male, adult 221,200 Schiller: Compter rendus de PAcademic dcs Sciences, Paris, 1889.* Die Functionen der Gangliemellen des Halsmarkes, Haag, 1891. CENTRAL NERVOUS SYSTEM. 729 Here, as in the frog, the apparent increase must be looked upon as due tothe gradual development of elements present from an early date. Increase in the Fibres of the Cortex.—The area of the cerebral cortex(see Fig. 205) varies according to several conditions, but in general the morevoluminous the cerebral hemispheres the greater its extent. That which cov-ers the walls of the sulci has in man about twice the extent of that directlyexposed on the surface of the Fig. 205.—Diagram illustrating the extent of the cerebral cortex. The outer square {E) shows a sur-face approximately ^V of 2352 sq. cm. in extent; the inner square (A) has two-thirds of this area, and isthe proportion of the cortex sunken in the fissures. 2352 sq. cm. is approximately the area of the entirecortex in a male brain weighing 1360 grams. In the cortex of the human cerebral hemispheres it has been shown byVulpius that the number of fibres in the different layers is greater at thethirty-third year than at earlier periods, and in old age the number is againdecreased. At exactly what age decrease sets in is not to be determined fromthese observations. They show, simply, that in general the number of fibreswas less at seventy-nine years than at thirty-three years. In a similar way Kaes^ has compared the development of the thickness ofthe cortical fibre-layers in a youth of eighteen years as contrasted with a manof thirty-eight years, and
Size: 1586px × 1574px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookautho, bookcentury1800, bookdecade1890, booksubjectphysiology
