During the embryonic development of higher animals (from flat worms to humans, in the beginning we all look the same), three primary layers of cells forms, germ layers, which give rise to all tissues and organs in the animal. The three layers are called ectoderm, mesoderm and endoderm (see below) and it is the mesoderm which is the origin of fascia, skeletal, cartilage and muscle, all components which are associated with locomotion. More primitive animals have only one or two germ layers, they are lacking in mesoderm. When the human embryo is about two to three weeks old, the fascia begins to form from the mesoderm. The three germ layers are;
Ectoderm – The outer (ecto) layer, form the outer skin, hair and nails, the nervous system, ectochrine glands and the dentin and tooth enamel.
Mesoderm – The middle layer, form the fascia. This layer also forms all kind of muscles (skeletal, smooth and cardiac), bone tissue, cartilage, dermis and hypodermis, circulatory system, blood cells, lymphatic system, spleen, mesentery, adipose tissue, notochord, meninges (membranes of the brain and spinal cord), urogenital system, kidneys and more.
Endoderm – The inner layer, form the epithelial inner layer of the whole digestive tract, glands like liver and pancreas, respiratory system, bladder, thyroid and thymus.
First to develop from the mesoderm is the mesenchyme, an embryonic connective tissue. It consists of stellate cells with long spurs, with which they communicate with each other. The extra cellular matrix (ECM), between these cells, is a light fluid with thin embryonic fibers of collagen type III. Most of this ECM fluid consists of hyaluronan and water.
Some research wants to claim that the fascia can be found in the ectoderm (van der Wal, 2009). Recent research has also found a fascial link between fascial fibers of muscles in the poll, sensory nerves and the dura mater (the outer of the meninges), called the myodural bridge (Hack et al, 1995), (Scali et al, 2011, 2013, 2015), (Zheng et al, 2014, 2018). The same connection has now been found in horses and several other mammals, as well as in chickens and reptiles (Elbrønd & Schultz, 2019), (Zheng et al, 2017), (Dou et al, 2019), (Zhang et al, 2016). More about this in another item.
