Lateral plate mesoderm is a type of mesoderm

Mesoderm

In all bilaterian animals, the mesoderm is one of the three primary germ cell layers in the very early embryo. The other two layers are the ectoderm and endoderm , with the mesoderm as the middle layer between them.The mesoderm forms mesenchyme , mesothelium, non-epithelial blood corpuscles and...

 that is found at the periphery of 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...

.

Division into layers

It will split into two layers, the somatic layer/mesoderm and the splanchnic layer/mesoderm

• The somatopleuric layer forms the future body wall.
• The splanchnopleuric layer forms the circulatory system
  Circulatory system
  The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...
  
   and future gut wall.

Spaces within the lateral plate are enclosed and forms the intraembryonic coelom

Coelom

The coelom is a fluid-filled cavity formed within the mesoderm. Coeloms developed in triploblasts but were subsequently lost in several lineages. Loss of coelom is correlated with reduction in body size...

.

It is formed by the secretion of BMP-4

Bone morphogenetic protein

Bone morphogenetic proteins are a group of growth factors also known as cytokines and as metabologens . Originally discovered by their ability to induce the formation of bone and cartilage, BMPs are now considered to constitute a group of pivotal morphogenetic signals, orchestrating tissue...

 by the ectoderm.

Serosal mesoderms

Lateral plate mesoderm gives rise to the serosal mesoderms.

• forms a ventral layer associated with endoderm
  Endoderm
  Endoderm is one of the three primary germ cell layers in the very early embryo. The other two layers are the ectoderm and mesoderm , with the endoderm as the intermost layer...
  
  , the splanchnopleuric mesoderm. This forms the viscera and heart
• forms a dorsal layer associated with ectoderm
  Ectoderm
  The "ectoderm" is one of the three primary germ cell layers in the very early embryo. The other two layers are the mesoderm and endoderm , with the ectoderm as the most exterior layer...
  
  , the somatopleuric mesoderm. This forms the body wall lining and dermis.
• Abdominal portion becomes contained in dorsal mesentery
  Dorsal mesentery
  The portion of mesentery attached to the greater curvature of the stomach is named the dorsal mesentery , and the part which suspends the colon is termed the mesocolon....
  
  , part of the serosal mesoderm.
• When the two layers form, a cardiogenic plate is visible. Later, this will form the myocardial primordium, which will contribute to the tubular heart.

Cavities

In the 4th week the coelom divides into pericardial, pleural and peritoneal cavities.

• First partition: is the septum transversum
  Septum transversum
  The septum transversum is a thick mass of cranial mesenchyme that gives rise to parts of the thoracic diaphragm and the ventral mesentery of the foregut in the developed human being.- Origins :...
  
  .

• This will be translocated later into the diaphragm and ventral mesentery
  Ventral mesentery
  -Development:The cephalic portion of the septum transversum takes part in the formation of the diaphragm, while the caudal portion into which the liver grows forms the ventral mesentery ....
  
  .
• Divides the coelom
  Coelom
  The coelom is a fluid-filled cavity formed within the mesoderm. Coeloms developed in triploblasts but were subsequently lost in several lineages. Loss of coelom is correlated with reduction in body size...
  
   into primitive pericardial and peritoneal cavities

• pleuropericardial folds appear on the lateral wall of primitive pericardial cavity, which will eventually cause a partition to form the pericardial and pleural cavities.
• Communication between these partitions formed by the pericardioperitoneal canals. However, pleuroperitoneal membranes will grow to fuse with the septum transversum to close off these canals.

• At day 22, lung buds
  Lung buds
  The cephalic part of the laryngo-tracheal tube becomes the larynx, and its next succeeding part the trachea, while from its caudal end two lateral outgrowths, the right and left respiratory buds or lung buds, arise, and from them the bronchi and lungs are developed.-External links:* *...
  
  form, remaining ensheathed in a splachnopleuric mesoderm

Limb Development

Cells from the lateral plate mesoderm and the myotome migrate to the limb field and proliferate to create the limb bud. The lateral plate cells produce the cartilaginous and skeletal portions of the limb while the myotome cells produce the muscle components. The lateral plate mesodermal cells secrete a fibroblast growth factor (FGF7 and FGF10, presumably) to induce the overlying ectoderm to form an important organizing structure called the apical ectodermal ridge (AER).The AER reciprocatively secretes FGF8 and FGF4 which maintains the FGF10 signal and induces proliferation in the mesoderm. The position of FGF10 expression is regulated by Wnt8c in the hindlimb and Wnt2b in the forelimb. The forelimb and the hindlimb are specified by their position along the anterior/posterior axis and possibly by two T-box containing transcription factors: Tbx5 and Tbx4, respectively.

See http://en.wikipedia.org/wiki/Limb_development for more information