Morphologic and physiologic changes during the neonatal period are coming to constitute a nodal area of research. While the bulk of the literature on the human newborn infant has related to the loss in weight following birth,1 investigation has also been made of such problems as changes in size of the uterus, weight of the adrenal glands,2 capacity of the stomach3 and calcium metabolism of bones4 and teeth.5
It is the purpose of this paper to report a study on changes of the size and contour of the thorax during the first postnatal week. Specifically, attention will be given to (a) the absolute width and depth of the thorax and (b) the trend of change in thoracic shape expressed by the ratio chest depth × 100/chest width.
The subjects were 68 newborn white infants, 36 boys and 32 girls, obtained through the department of