Separation of the Embryo

From WikiMD
Jump to navigation Jump to search

Henry Gray (1821–1865). Anatomy of the Human Body. 1918.

9. Separation of the Embryo

The embryo increases rapidly in size, but the circumference of the embryonic disk, or line of meeting of the embryonic and amniotic parts of the ectoderm, is of relatively slow growth and gradually comes to form a constriction between the embryo and the greater part of the yolk-sac. By means of this constriction, which corresponds to the future umbilicus, a small part of the yolk-sac is enclosed within the embryo and constitutes the primitive digestive tube.


image21.gif


FIG. 21– Section through the embryo which is represented in Fig. 17. (After Graf Spee.)

The embryo increases more rapidly in length than in width, and its cephalic and caudal ends soon extend beyond the corresponding parts of the circumference of the embryonic disk and are bent in a ventral direction to form the cephalic and caudal folds respectively (Figs. 26 and 27). The cephalic fold is first formed, and as the proamniotic area (page 47) lying immediately in front of the pericardial area (page 47) forms the anterior limit of the circumference of the embryonic disk, the forward growth of the head necessarily carries with it the posterior end of the pericardial area, so that this area and the buccopharyngeal membrane are folded back under the head of the embryo which now encloses a diverticulum of the yolk-sac named the fore-gut The caudal end of the embryo is at first connected to the chorion by a band of mesoderm called the body-stalk but with the formation of the caudal fold the body-stalk assumes a ventral position; a diverticulum of the yolk-sac extends into the tail fold and is termed the hind-gut Between the fore-gut and the hind-gut there exists for a time a wide opening into the yolk-sac, but the latter is gradually reduced to a small pear-shaped sac (sometimes termed the umbilical vesicle), and the channel of communication is at the same time narrowed and elongated to form a tube called the vitelline duct


Gray's Anatomy


W8MD logo

Ad. Tired of being overweight?. W8MD's insurance weight loss can HELP*

Lose weight King of Prussia, PA | Lose weight NYC | Lose weight NJ | Lose weight Philadelphia | Advertise
Other languages:
English

Disclaimer: The entire contents of WIKIMD.ORG are for informational purposes only and do not render medical advice or professional services. If you have a medical emergency, you should CALL 911 immediately! Given the nature of the wiki, the information provided may not be accurate, misleading and or incorrect. Use the information on this wiki at your own risk! See full Disclaimer. * Individual results may vary for weight loss from our sponsors.

Our sponsors WikiMD is supported by W8MD weight loss, sleep and medical aesthetic centers.