Title: Embryology
Identifier: embryology00bart (find matches)
Year: 1949 (1940s)
Authors: Barth, Lester G. (Lester George), 1905-1979
Subjects: Embryology; Embryology; genealogy
Publisher: New York, Dryden Press
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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278 EMBRYOLOGY
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Fig. 186. The embryo at about one month old. (From Julius Kollman, Handatlas der Entwkklun gs geschicht e des Menschen. Verlag von Gustav Fischer, Jena.) and the otocyst is pear-shaped. The neural folds have closed completely, and a well-developed brain has formed. The heart shows the same spiral arrange- ment as in the chick embryo. At four weeks the embryo is about 5 mm. long and weighs about 20 mg. (Fig. 186). At this stage 40 somites are present, the arm and leg buds have formed, and the embryo corresponds roughly to about a three- to four-day chick embryo. The neural tube is completely closed now, and the divisions of the brain are more sharply defined. The optic primordia have become optic cups, and the lens is forming. The auditory placode has formed the otocyst, and the olfactory placodes are present as thickenings of the head ectoderm. In the nervous system nerves are beginning to develop in the motor region of the spinal cord and from the spinal ganglia. In the region of the pharynx the endoderm has formed five visceral pouches and the primordia of the tongue are present. The laryngotracheal groove has developed into paired lungs and trachea, and the thyroid sacs are now well defined. The liver is clearly developed, with its ducts and with the primordium for the gall bladder. The pancreas is represented by diverticula from the midgut. There is a clear differentiation between the esophagus, stomach, and intestine.

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