Mesenchyme

Mesenchyme (also known as embryonic connective tissue) is the mass of tissue that develops mainly from the mesoderm (the middle layer of the trilaminar germ disc) of an embryo. Viscous in consistency, mesenchyme contains collagen bundles and fibroblasts. Mesenchyme later differentiates into blood vessels, blood-related organs, and connective tissues.

Embryonic connective tissue (mesenchyme):
 * Derives from the embryonic mesoderm
 * Consists of loosely-packed, unspecialized cells set in a gelatinous extracellular matrix
 * Develops into other types of tissues: connective, bone, cartilage
 * Develops into other types of structures and systems: blood cells, endothelial cells, smooth muscle cells, circulatory system, lymphatic system.

All organs in the body contain mesenchyme.

Ectomesenchyme
Ectomesenchyme has similar properties to mesenchyme. The major difference is that ectomesenchyme is usually considered to arise from neural crest cells, which are a critical group of cells that form in the cranial region during early human development. Thus, ectomesenchyme plays a critical role in the formation of the hard and soft tissues of the head and neck such as bones, muscles and most importantly the branchial arches.