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Morphologic Peculiarities

brain, weight, grams, third, differences, adult, newborn and brains

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MORPHOLOGIC PECULIARITIES Aside from the intimate adhesions between the dura and the bones of the cranial vault, the absence of Pacchionian bodies and the small ness and friability of all the structures, the mere opening of the skull and vertebral canal presents in children no peculiarity worthy of note. The cfisposition and form of the various structures, their relations to thc .11rrn-tintiir nfrrt. DI, 1110 .n :IR ill tilP .1111t. OnIV tile ver tebral canal are slight differences to be observed. It is well known that the adult spinal cord terminates at a point eorresponding to about the lower third of the first, or to the superior border of the second, lumbar vertebra. In the fcetus, on the contrary, the cord fills the vertebral canal entirely and it is only in the later stages of intra-uterine life and owing to the more rapid growth of the vertebral column, that it gradually recedes. In the newborn, the end of the corms medulla/is still lies in the cavity of the third lumbar vertebra; the ultimate rela tions however, beeome more or less fully established during the first phase of life. This modification in the relations between the spinal cord and the vertebral eolumn affords an explanation of the fact, so significant to the surgeon, that in young children and particularly in infants, the spinal nerves, especially those of the lower segments, pur sue, in order to reach their respective foramina, a different course than in the adult, being mueli less obliquely directed.

On section, the eut surface of the central nervous organs more particularly of the prematurely-born, has a very distinct grayish hue whieh is not to be seen in the brains of older individuals.

The brain of the newborn is relatively large. Whereas most of the organs of the body weigh, at birth, only the tenth to the fourteenth part of their ultimate weight, the brain has already- reached the fourth part of its ultimate weight. In proportion also to total body weight is its volume greater in the infant than in the adult; the proportion being as 1: 85 and even 1:75 according to Zichen's estimates, against 1: 42 in the male, and 1:40 in the female, adult. Mies places the abso lute weight of the brain of the newborn at about 340 grams in males and 330 grams in females. These figures, he obtained from statis tics published prior to 1894, and based on single weighings of brains of the most miscellaneous source (brains of Germans, Romans, Slays, as well as of subjects belonging to remote countries), having thus used an anthropologic material of an insufficiently equivalent and uniform character. Ziehen, Marchand and others, consider that these

figures are rather too low.

It must certainly be stated that among healthy Germans the average 'weight of the brain of the newborn is decidedly higher (between 350 and 370 grams). With the progress of development, the weight of the brain steadily increases and may even reach 1400 grams; the average figure varying between 1250 and 1275 grams. According to Mies, the maximum figure would be only 12:30 grams, and 900 grams would represent the average weight of a fairly well developed brain. The first third of this increase in the weight of the brain had taken place (in the author's cases) by the ninth month, the second third by the second quarter of the third year, of extra-uterine life (see Figs. 21 and 22); thus, the original weight of the brain was doubled by the end of the third quarter of the first year and trebled before the ex piration of the third year (Marchand). According to this author, the ultimate weight of the brain is attained between the nineteenth and twentieth year.

At all ages the average weight of the brain is lower in females than in males. In consequence of the relatively more vigorous development of the male brain, this difference in brain weight between the sexes, which, at birth, only- equals from 10 to 15 grams, increases to 120 grams and more in adult life.

Differences in brain weight also occur which are not dependent upon eorresponding differences in total body weight or general develop ment, as they are observed in subjects belonging to the same sex, of the same age and even of the same weight. They are to be considered simply as the expression of some particular individual (most often hereditary) tendency. Even in the brains of the newborn, differences of from 50 to 70 grams may be observed, as also, variations in the capacity of the cranial cavity, which, already in the third week, may amount to as inueh as 7.5 and 100 c.c., and even more. As age ad vances the scope of this physiologic variation becomes even greater. In children of about three months, differences in brain weight of from 200 to 300 grams have been recorded. Very frequently individuality finds expres.sion in a preeocious development of the brain. Brains weighing as much as 12SO grams have been observed in children of only three years, and from 1350 to 1400 grams, in boys of five years. Excessively high figures have also been occasionally recorded; in Lorey's case (a child of six years) the brain weighed 1540 grams.

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