Milk line
Encyclopedia
The milk lines are two parallel lines, formed by thickenings of the epidermis (the mammary ridge) along the ventral surface of mammal
s of both sexes. They extend from the upper limbs (arms) to the lower limbs (legs) and are developed in the embryo
. They give rise to the mammary gland
s and nipple
s but are otherwise usually not visible in the adult.
nic stage. In many mammals, these glands first appear as elevated ridges along the milk lines, which then separate into individual buds located in regions lateral to the ventral midline. The location of these buds varies according to species; they are located in the thoracic
region in primates, in the inguinal
area in ungulate
s, and along the entire length of the trunk in rodent
s and pig
s.
s, milk lines appear in the seventh week of embryonic development. After initial development of the milk lines they go into remission.
Nipples develop on the milk lines of mammals. Most humans have two nipples, but in some cases more than two will develop. In most cases, these additional nipples grow along the milk line.
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s of both sexes. They extend from the upper limbs (arms) to the lower limbs (legs) and are developed in the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
. They give rise to the mammary gland
Mammary gland
A mammary gland is an organ in mammals that produces milk to feed young offspring. Mammals get their name from the word "mammary". In ruminants such as cows, goats, and deer, the mammary glands are contained in their udders...
s and nipple
Nipple
In its most general form, a nipple is a structure from which a fluid emanates. More specifically, it is the projection on the breasts or udder of a mammal by which breast milk is delivered to a mother's young. In this sense, it is often called a teat, especially when referring to non-humans, and...
s but are otherwise usually not visible in the adult.
Mammary gland development
Mammary glands begin developing during the embryoEmbryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
nic stage. In many mammals, these glands first appear as elevated ridges along the milk lines, which then separate into individual buds located in regions lateral to the ventral midline. The location of these buds varies according to species; they are located in the thoracic
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
region in primates, in the inguinal
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
area in ungulate
Ungulate
Ungulates are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive...
s, and along the entire length of the trunk in rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s and pig
Pig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
s.
Milk lines in humans
In humanHuman
Humans are the only living species in the Homo genus...
s, milk lines appear in the seventh week of embryonic development. After initial development of the milk lines they go into remission.
Nipples develop on the milk lines of mammals. Most humans have two nipples, but in some cases more than two will develop. In most cases, these additional nipples grow along the milk line.
See also
- Supernumerary nippleSupernumerary nippleA supernumerary nipple is an additional nipple occurring in mammals, including humans...
- Mammary glandMammary glandA mammary gland is an organ in mammals that produces milk to feed young offspring. Mammals get their name from the word "mammary". In ruminants such as cows, goats, and deer, the mammary glands are contained in their udders...
- BreastBreastThe breast is the upper ventral region of the torso of a primate, in left and right sides, which in a female contains the mammary gland that secretes milk used to feed infants.Both men and women develop breasts from the same embryological tissues...
- NippleNippleIn its most general form, a nipple is a structure from which a fluid emanates. More specifically, it is the projection on the breasts or udder of a mammal by which breast milk is delivered to a mother's young. In this sense, it is often called a teat, especially when referring to non-humans, and...
- Teat
- UdderUdderAn udder is an organ formed of the mammary glands of female quadruped mammals, especially ruminants such as cattle, goats, sheep and deer. The udder is a single mass hanging beneath the animal, consisting of pairs of mammary glands...
- LactationLactationLactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process occurs in all female mammals, however it predates mammals. In humans the process of feeding milk is called breastfeeding or nursing...
- MilkMilkMilk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...