from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The middle embryonic germ layer, lying between the ectoderm and the endoderm, from which connective tissue, muscle, bone, and the urogenital and circulatory systems develop.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. One of the three tissue layers in the embryo of a metazoan animal. Through embryonic development, it will produce many internal organs of the adult, e.g. muscles, spine and circulatory system.
from the GNU version of the Collaborative International Dictionary of English
- n. The layer of the blastoderm, between the ectoderm and endoderm; mesoblast. See Illust. of blastoderm and ectoderm.
- n. The middle body layer in some invertebrates.
- n. The middle layer of tissue in some vegetable structures.
from The Century Dictionary and Cyclopedia
- n. The middle germinal layer of the three-layered embryo of any metazoic animal, lying between the endoderm and the ectoderm.
- n. In botany, the middle layer of tissue in the shell of the spore-case of an urn-moss.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. the middle germ layer that develops into muscle and bone and cartilage and blood and connective tissue
Sorry, no etymologies found.
The outer layer of this ‘gastrula’ is called the ectoderm, the inner layer is the endoderm, and there are also some cells thrown into the space between the ectoderm and endoderm, which are called mesoderm.
In contrast to flies, which have a clearly segmented ectoderm, the mesoderm is the primary vertebrate tissue that is organized in a metameric pattern.
According to Haeckel, the origin of the generative products in the mesoderm is a heterotopic phenomenon, for he considers that they must have originated phylogenetically in one of the two primary layers, ectoderm or endoderm.
Outside the amniotic ectoderm is a thin layer of mesoderm, which is continuous with that of the somatopleure and is connected by the body-stalk with the mesodermal lining of the chorion.
The cells of this layer proliferate rapidly, and extending medialward surround the notochord; at the same time they grow backward on the lateral aspects of the neural tube and eventually surround it, and thus the notochord and neural tube are enveloped by a continuous sheath of mesoderm, which is termed the membranous vertebral column.
These pairs of "cubes" of the mesoderm are the first traces of the primitive segments or somites, the so-called "protovertebrae."
Down at the bottom, on either side of the hole, is a tissue called the presomitic mesoderm
Note the absence of Hoxa13 and Hoxd13 from the corn snake mesoderm and the absence of Hoxd12 from the snake genome.
But technologies that let researchers track cells during embryo development finally allowed them to watch the neural crest's development, culminating in the attachment of head to the body at its front, while the back attachment springs from the mesoderm tissue layer.
For example, the outer skin and nervous system come from the ectoderm; the guts and other internal organs come from the endoderm; and the mesoderm furnishes muscle and bone.