Paper - A Human Embryo of Thirteen Somites
Embryology - 26 Apr 2024    Expand to Translate
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Wallin IE. A Human Embryo of Thirteen Somites Am J Anat. 1913;
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A Human Embryo Of Thirteen Somites
Ivan E. Wallin
Anatomical Laboratory, Bellevue Hospital Medical College, New York City
Seven Figures
The embryo which forms the basis of this work was given to
me by Dr. Rudolph Boencke in the spring of 1911. It has been
placed in the collection of the Department of Anatomy at the
University and Bellevue Hospital Medical College and is called
embryo no. 4.
The embryo was aborted two weeks after the last menstrual
period. There was no record of coitus. After fixation and with
the amnion intact the embryo measured 2.3 mm. in length. It
was cut into transverse sections 5 u in thickness, and stained
with iron‘ haematoxylin. The embryo yielded 287 sections.
Wax plate reconstructions were made of the complete embryo,
the heart, the foregut, also of the caudal part of the medullary
tube with the hind-gut and the belly stalk vessels. A graphic
reconstruction was made representing the embryo cut in the
mid-sagittal plane. All the reconstructions were made at a magnification of 200.
The embryo appears to be normal in every respect and the
following points of structure have been determined.
External Form
In its general configuration this embryo is very similar to Pfannenstiel III described by Low (’08). The body has a regu- lar dorso-ventral curve and has a slight twist so that the head is situated to the right of the mid-sagittal plane. The yolk sac communicates with the primitive gut by means of an extensive yolk stalk. The latter has its greatest diameter in the cephalo~caudal direction and its lateral width is greatest at the cephalic end. Caudal and to the right of the yolk stalk the belly stalk leaves the embryo passing ventrally and curving to the right and caudad. Lateral to the yolk stalk the embryonic coelom has an extensive communication with the extra-embryonic coelom.
The heart produces a prominent bulging of the right side of
the body immediately caudad to the head. The most prominent
part of the bulging marks the flexure in the heart tube between
the bulbus cordis and the ventricle. ‘The neck flexure has not
advanced to any prominent degree. There are two prominences
on the dorsal surface of the head region, one at the cephalic end
of the mid—brain and the other at the cephalic end of the hindbrain. Caudally the body curves gradually in a ventral direction. There is no distinct caudal flexure.
The medullary tube is open to the exterior at both ends. The
cephalic neuropore exhibits an unusual appearance for an embryo
of this age. It is Very wide and gives a great breadth to the
head when viewed from the ventral aspect. The lateral lips of
this neuropore curve dorsally and form the ventral boundary of
a deep groove which is directed cephalo—caudally. The caudal
end of this groove runs into the stomodeum. This part of the
nervous system which represents the forebrain has not kept
apace with the development of the remainder of the tube. It
apparently is a persistence of the condition which is present in
an earlier stage of development. Eternod’s (’95) embryo of
eight somit'es and the embryo of seven somites described by
Dandy (’10) exhibit cephalic neuropores which appear to be in
about the_same stage of development.
There are no indications of otic invaginations. Two pairs of
entodermal pouches are in contact with the ectoderm. The
points of contact are indicated on the surface by shallow depres-
sions. In figure 2 their positions have been indicated on the surface by broken lines.
The amnion lies close on to the body of the embryo. The
head fold crosses the ventral aspect of the heart at about its
middle. The lateral folds follow the lateral lips of the coelom.
The tail fold is situated on the dorsal aspect of the belly stalk.
Cite this page: Hill, M.A. (2024, April 26) Embryology Paper - A Human Embryo of Thirteen Somites. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_A_Human_Embryo_of_Thirteen_Somites
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
