The longitudinal growth of the neuromeres and the resulting brain in the human embryo.

The growth of the human brain during the embryonic period was assessed in terms of longitudinal measurements in staged embryos. Precise graphic reconstructions prepared by the onerous point-plotting method were considered to be the most reliable, and 23 were examined in detail. A distinction is necessary between measurements of the brain (cerebral diameters) and those of the skull (osseous diameters), and also between those of the folded brain in situ, studied here, and the later relatively straightened brain.

The initial appearance of the cranial nerves and related neuronal migration in staged human embryos.

The initial development of the cranial nerves was studied in 245 human embryos of stages 10-23 (4-8 postfertilizational weeks). Significant findings in the human embryo include the following. (1) Neuronal migration is a characteristic feature in the development of all the cranial nerves at stages 13-18, with the exception of the somatic efferent group.

Developmental stages in human embryos: revised and new measurements.

The staging of human embryos, as distinct from seriation, depends on a morphological scheme devised by Streeter and completed by O'Rahilly, who proposed the term Carnegie stages. To avoid misconceptions and errors, and to place new findings in perspective, it is necessary to summarize the essentials of the Carnegie system: (1) Twenty-three stages cover the embryonic period, i. e.

Significant features in the early prenatal development of the human brain.

A review of the early prenatal development of the human brain has been prepared following a long-standing investigation of 192 embryos. The precise sequence of developmental events has been traced with the aid of accurate morphological staging. The three major divisions of the brain appear in the walls of the completely open neural groove at 3(1/2) postfertilizational weeks (stage 9).

The development of the neural crest in the human.

The first systematic account of the neural crest in the human has been prepared after an investigation of 185 serially sectioned staged embryos, aided by graphic reconstructions. As many as fourteen named topographical subdivisions of the crest were identified and eight of them give origin to ganglia (Table 2). Significant findings in the human include the following.

The amygdaloid complex and the medial and lateral ventricular eminences in staged human embryos.

The amygdaloid complex was investigated in 36 serially sectioned staged human embryos, including 20 impregnated with silver. This is the first such account based on graphic reconstructions, 28 of which were prepared. Significant findings in the human include the following.

Segmentation in staged human embryos: the occipitocervical region revisited.

The first seven somites, the rhombomeres, and the pharyngeal arches were reassessed in 145 serially sectioned human embryos of stages 9-23, 22 of which were controlled by precise graphic reconstructions. Segmentation begins in the neuromeres, somites and aortic arches at stage 9. The following new observations are presented.

The two sites of fusion of the neural folds and the two neuropores in the human embryo.

Background: Since reports on a pattern of multiple sites of fusion of the neural folds in the mouse appeared, it has been widely assumed that a similar pattern must be valid for the human. In the absence of embryological evidence, claims have been made that such a pattern can be discerned by classifying neural tube defects.

Methods: The neural folds and tube, as well as the neuropores, were reassessed in 98 human embryos of Stages 8-13; 61 were controlled by precise graphic reconstructions.