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From Embryology

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Fig. 89. Human embryo 11 mm long (31-34 days)

His.

Figure 89 shows an embryo of 11 mm. All the flexures are slightly reduced except the cephalic. The cephalic flexure, which primarily affects the embryonic brain, persists as the mid-brain flexure of the adult. Two slight concavities have appeared in the dorsal profile, the occipital depression and the cervical depression. The latter becomes more conspicuous as development proceeds and persists as the depression at the back of the neck in the adult. The first branchial arch is a strong feature of the head, the maxillary process being especially prominent. This process has grown forward to form intimate contact with the nasal region. The second arch now hides the third and fourth arches, and the depression behind the second is known as the precermcal sinus. The first groove can be more readily appreciated as the site of the external auditory meatus, as can also the surrounding parts of the first and second arches be better appreciated as rudiments of the concha. The distal part of the fore-limb bud is flattened like a paddle, and the radial depressions in it mark the boundaries between the digits. In the proximal portion the fore-arm and arm are faintly indicated. The hind-limb bud is divided by a constriction into a proximal and distal portion; the latter is the beginning of the foot. During development the fore-limb is always at a slightly more advanced stage than the hind-limb. The ventral rotundity of the body is pronounced.


--Mark Hill 08:39, 13 April 2011 (EST)The size and timing of this historic description (stage 14) is earlier than the external appearance suggests (stage 16-17), particularly that of the limbs.


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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)

Reference

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



Cite this page: Hill, M.A. (2024, February 25) Embryology Bailey089.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Bailey089.jpg

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