GROWTH OF GRAY AND WHITE MATTER IN THE THORACIC SEGMENTS OF THE CHICK EMBRYO SPINAL CORD

Abstract

SUMMARY The following morphometric data on the thoracic segments of the spinal cord of the chick embryo (from 4 days to hatching) are reported: length of the segments, volume of the gray and white matter, average section area of the gray and white matter, number of mitoses in the neural epithelium. Data on the number of nerve, glial and vascular cells in each segment at hatching are also given. The development of the gray matter is discussed mainly in terms of the differential growth between the segments. At 4 days of incubation the cranial and caudal segments of the series are already bigger than the central ones because of their greater length, while the section area is almost equal throughout the thoracic cord. Subsequent growth of the central segments takes place mainly in length, whereas the extreme ones grow especially in width, so that, at hatching, the latter exhibit a greater section area but a shorter length, as compared to the former. On the whole, differential volume growth to advantage of the...