The lateral plate mesoderm (LPM) is a pair of neurula-stage mesodermal sheets located lateral to the intermediate mesoderm. In the third week of human development (day E7.0 in mouse), small gaps formed in the lateral plate mesoderm merge to form a larger cavity called the intraembryonic coelom. This cavity splits the lateral plate mesoderm into the splanchnic mesoderm, located above (dorsally) the endoderm, and the somatic mesoderm, located under (ventrally) the ectoderm.
The splanchnic mesoderm, which is adjacent to the endoderm and yolk sac, forms the heart as well as the visceral layer of the serous pericardium and blood vessels. It also contributes to the smooth muscle and connective tissues of the respiratory and digestive organs. The somatic mesoderm, which is adjacent to the ectoderm and amnion, gives rise to the bones, ligaments, blood vessels, and connective tissue of the limbs.
The LPM also contributes to the development of dermis, pulmonary system components (lungs, larynx, bronchi), urinary system (bladder and urethra, glomular capillaries of Bowman's capsule), spleen, adipose tissue, viscerocranial components of the head (including cartilaginous structures of the face and neck, mouth, tongue, pharynx, nasal cavities and portions of the ears), blood, lymphatic system and various other tissues, including the diaphragm, epithelium and mesenteries.