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Primarily subhead 12 Days of Christmas under Catholic and Culture. Bowler, Gerald (2000). The World Encyclopedia of Christmas. Toronto: M&S. ISBN 978-0-7710-1531-1. OCLC 44154451. Caulkins, Mary; Jennie Miller Helderman (2002). Christmas Trivia: 200 Fun & Fascinating Facts About Christmas. New York: Gramercy. ISBN 978-0-517-22070-2. OCLC 49627774.
In humans, blastocyst formation begins about five days after fertilization when a fluid-filled cavity opens up in the morula, the early embryonic stage of a ball of 16 cells. The blastocyst has a diameter of about 0.1–0.2 mm and comprises 100-200 cells following 7-8 rounds of cleavage (cell division without cell growth).
At maturity, there are roughly 30 trillion cells, and 38 trillion bacteria in the body, [3] [4] an estimate arrived at by totaling the cell numbers of all the organs of the body and cell types. The skin of the body is also host to billions of commensal organisms as well as immune cells. [5] Not all parts of the body are made from cells.
Eight-cell embryo, at three days. The beginning of the cleavage process is marked when the zygote divides through mitosis into two cells. This mitosis continues and the first two cells divide into four cells, then into eight cells and so on. Each division takes from 12 to 24 hours.
Labeled anatomy of the human vulva and nearby structures. The vulva is of all of the external parts and tissues and includes the following: [3] Clitoris: an organ located at the top of the vulva. It consists of the body and its pea-shaped glans that is protected by the clitoral hood.
Implantation bleeding occurs between 7 and 14 days after fertilization, [56] and is a small amount of light vaginal bleeding or spotting that can occur in early pregnancy due to the blastocyst penetrating the lining of the uterus during implantation.
[4] Parts of the adult navel include the "umbilical cord remnant" or "umbilical tip", which is the often protruding scar left by the detachment of the umbilical cord. This is located in the center of the navel, sometimes described as the belly button. Around the cord remnant is the "umbilical collar", formed by the dense fibrous umbilical ring ...
The semantic field of the term crotch is sometimes expanded to include objects which have shapes similar to that of the anatomical human crotch. [9] This may include botanical structures such as the area where tree branches are joined together [10] or mechanical structures which fork or branch or where ramification takes place. [11]