Original file(924 × 774 pixels, file size: 129 KB, MIME type: image/jpeg)

Fig. 83. Ventral and dorsal view of human embryo with 8 pairs of mesodermal somites

Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
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)

2.11 mm. CRL

(a) Ventral view, the yolk sac has been removed.

(b) dorsal view, the amnion has been removed, merely the cut edge showing.

Eternod. From models by Ziegler.

Somewhat more advanced than the von Spee embryo is one described by Eternod (Fig. 83). Eternod's embryo is 2.11 mm. in length and possesess eight primitive segments. The figure shows the amnion cut away on the dorsal side and the yolk sac on the ventral side. The body is more markedly cylindrical than the preceding stage, and more elongated. The constriction between the embryo and the yolk sac is well marked, and the narrower yolk stalk can be better appreciated. At the caudal end the belly stalk forms the attachment to the chorion. The neural folds are partly fused to form the neural tube. The cephalic end of the neural plate is notably larger, a character which already indicates the beginning of the head. One might say that the yolk stalk is becoming smaller; but as a matter of fact the diminution is more apparent than real. The apparent diminution is caused by the relatively more rapid increase in size of the embryonic body and yolk sac. At this point it should be mentioned that the bending and tucking under the body of the lateral body walls naturally results in the contact and eventual fusion of the two sides in the mid- ventral line. In this manner the ventral body wall is formed. The line of fusion is significant in its relation to certain malformation : For instance, the fusion is sometimes defective or incomplete, allowing some of the viscera to protrude. (See Chap. XX on "Teratogenesis.") If the fusion is normal the ventral body wall is complete and closed except at the attachment of the umbilical cord through which pass the blood vessels that carry nutriment to the embryo and waste products away from it.


The changes that occur in the simple cylindrical body after the ventral body wall is closed comprise the differentiation of the head, neck and trunk regions and the development of the extremities as appendages of the trunk. Even in Eternod's embryo (Fig. 83) the region where the brain is developing is greater in diameter than the other part of the embryo. Thus the beginning of the head is indicated by an increase in size due primarily to the growth of the brain. The end of the head region is bent ventrally almost at a right angle to the long axis of the embryo, the bend occurring in the mid-brain and being known as the cephalic flexure. This is the first of the flexures that appear as development proceeds. On the cephalic side of the yolk sac attachment is a protrusion which indicates the position of the heart in what now may be called the cervical region or neck. Between the protrusion caused by the heart and the fore-brain there is~a depression which foreshadows the oral and nasal cavities and is now called the oral fossa.


Links: Fig.83 in text


Text-Book of Embryology: Germ cells | Maturation | Fertilization | Amphioxus | Frog | Chick | Mammalian | External body form | Connective tissues and skeletal | Vascular | Muscular | Alimentary tube and organs | Respiratory | Coelom, Diaphragm and Mesenteries | Urogenital | Integumentary | Nervous System | Special Sense | Foetal Membranes | Teratogenesis | Gallery of All Figures
Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
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. (2020, September 24) Embryology Bailey083.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Bailey083.jpg

What Links Here?
© Dr Mark Hill 2020, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G

File history

Click on a date/time to view the file as it appeared at that time.

Date/TimeThumbnailDimensionsUserComment
current15:35, 18 January 2011Thumbnail for version as of 15:35, 18 January 2011924 × 774 (129 KB)S8600021 (talk | contribs)