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Non-human mammals [ edit ] The anatomy of the area surrounding an embryo or fetus is different in litter-bearing animals compared to humans: each unborn animal is surrounded by placental tissue and is lodged along one of two long uterine horns rather than in the center of the pear-shaped uterus found in a human female.
In mammals, the term refers chiefly to the early stages of prenatal development, whereas the terms fetus and fetal development describe later stages. [2] [4] The main stages of animal embryonic development are as follows: The zygote undergoes a series of cell divisions (called cleavage) to form a structure called a morula.
Gestation, called pregnancy in humans, is the period of time during which the fetus develops, dividing via mitosis inside the female. During this time, the fetus receives all of its nutrition and oxygenated blood from the female, filtered through the placenta , which is attached to the fetus' abdomen via an umbilical cord .
In mammals, pregnancy is the period of reproduction during which a female carries one or more live offspring from implantation in the uterus through gestation. It begins when a fertilized zygote implants in the female's uterus , and ends once it leaves the uterus.
Figure 1:In mammals, the quadrate and articular bones are small and part of the middle ear; the lower jaw consists only of dentary bone.. While living mammal species can be identified by the presence of milk-producing mammary glands in the females, other features are required when classifying fossils, because mammary glands and other soft-tissue features are not visible in fossils.
Bleeding and spotting are common during the luteal phase of the menstrual cycle, and early stages of pregnancy, but are unrelated to implantation. 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 ...
The fetuses of most mammals are situated similarly to the human fetus within their mothers. [41] However, the anatomy of the area surrounding a fetus is different in litter-bearing animals compared to humans: each fetus of a litter-bearing animal is surrounded by placental tissue and is lodged along one of two long uteri instead of the single ...
It is typical for mammals, but also occurs for some non-mammals. Mammals during pregnancy can have one or more gestations at the same time, for example in a multiple birth. [2] The time interval of a gestation is called the gestation period.