From Embryology

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Fig. 88. Human embryo with 28 primitive segments (7.5 mm)


In Fig. 88, showing an embryo of 7.5 mm with 27 primitive segments (somites), the head is somewhat larger in proportion to the body. This character becomes accentuated as development proceeds and is especially noticeable up to the time of birth. The cervical and sacral flexures are still sharp, but the dorsal flexure is not quite so prominent. From now on, the body becomes more nearly straight. The rotundity of the ventral side of body is due to the heart and liver, the two organs now lying close together. The branchial arches are not actually smaller but appear less prominent. The second arch has enlarged and grown back over the third and fourth, partially hiding them. The limb buds' are larger; and the fore-limb bud now shows a transverse constriction dividing it into a proximal and a distal portion, the latter being the rudiment of the hand.

Links: Fig. 88 in text

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Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)


Bailey FR. and Miller AM. Text-Book of Embryology (1921) New York: William Wood and Co.

Cite this page: Hill, M.A. (2024, June 22) Embryology Bailey088.jpg. Retrieved from

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