The first sequence illustrates the general subdivision of the mesoderm into extraembryonic and intraembryonic mesoderms. A uterus with a 5-day-old blastocyst is detailed. The next sequence shows the implantation of the blastocyst into the endometrium under moderate magnification. In the 8-day-old blastocyst, the bilaminar germ disc develops, and the trophoblastic lacunae appear. During the next three days, the extraembryonic mesoderm (magma reticulare) develops between the cytotrophoblast and the exocelomic membrane.

The next sequence shows a 13-day-old blastocyst. The extraembryonic mesoderm separates into the extraembryonic somatopleuric (somatic, parietal) and the extraembryonic splanchnopleuric (splanchnic, visceral) mesoderm. The diagram also reveals the repartition of the two kinds of the extraembryonic mesoderms along with the development of the chorion, chorionic cavity, primary chorionic villi, the bilaminar germ disc, the exocelomic cyst and numerous other details. The start of the development of the intraembryonic mesoderm is animated in an approximately 16-day-old embryo, which presents the extraembryonic and the intraembryonic mesoderms on the same diagram. In the meantime, the secondary chorionic villi develop when the extraembryonic somatopleuric mesoderm invades the primary chorionic villi.

The next sequence shows the development and the derivatives of the intraembryonic mesoderm under slightly higher magnification. The sequence starts with a description of a 9-day-old blastocyst. The hypoblastic cells slide along the exocelomic membrane to form the definitive yolk sac in a blastocyst at the end of the 2nd week. At the same time, the extraembryonic mesoderm divides into the somatopleuric and splanchnopleuric mesoderms. The next sequence animates the appearance of the intraembryonic mesoderm within the trilaminar germ disc in a 16 day-old embryo. During the next three days, the intraembryonic mesoderm connects with the extraembryonic mesoderm. The next sequence shows the differentiation of the intraembryonic mesoderm into somites with somitoceles, the intermediate mesoderm, and the lateral plate, which is in contact with the somato- and splanchnopleuric extraembryonic mesoderms. Further development of the mesoderm is animated in an approximately 20-day-old embryo: the somites (sclerotomes and dermomyotomes) differentiate and divide; the intermediate mesoderm and the lateral plateare now separated into the somato- and splanchnopleura. The lateral folding of the embryo brings the somato- and splanchnopleura into contact. Three days later, the somites separate from the intermediate mesoderm, which forms the nephrogenic cords. The same sequence depicts the differentiation of the somato- and splanchnopleura into the parietal and visceral peritoneum.

The following sequence demonstrates the migration of the mesodermal cells between the epiblast and the hypoblast as viewed from the amniotic cavity. A transversally cut 16-day-old embryo is shown. Then the amnion is cut, and the upper wall of the amniotic cavity is removed. The direction of the migration of the mesodermal cells is indicated with arrows, and the trilaminar germ disc is observed from above. From the primitive node and the primitive streak, the mesodermal cells spread between the hypoblast and the epiblast in the direction of buccopharyngeal membrane through the notochordal process of a 17-day-old embryo. Finally, in an 18-day-old embryo, the trilaminad germ disc is formed. From this disc, a sector is cut out and rotated toward the spectator to show its stratification into the ectoderm, the mesoderm with the notochord, and the endoderm.

The next sequence animates the evolution of the external form of the germ disc. From the presomite embryos over the course of the 16th, 19th day, and somite embryo at the 21st day, somites develop in parallel with the formation of the neural tube. Somites continue to appear along the neural tube from the 24th to the 27th day.

The next animation is dedicated to the differentiation and derivatives of the sclerotome. The first diagram shows a transversal section of an approximately 23-day-old embryo. During the next two days, in an approximately 25-day old embryo, the mesenchymal sclerotome cells migrate toward the notochord, surround it, and differentiate into hyaline cartilage. In an approximately 28-day-old embryo, the vertebral body forms around the notochord, and the dermomyotome subdivides into dermatome and the myotome.

In the sequence concerning the differentiation and derivatives of the dermatome, the migration of the mesenchymal dermatome cells toward the ectoderm of the dorsal region is shown in from days 28 to 30. The same sequence shows the migration of mesenchymal cells from the somatopleura, which move toward the ectoderm of the ventral region of the embryo. In both cases, these cells form the dermis and the hypodermis of the skin. The formation of the gut tunica muscularis from the splanchnopleuric mesenchymal cells is also animated. Two days later, the skin forms.

The development and the derivatives of the myotomes are animated under Myogenesis.

(This animation is essential for students of medicine, veterinary medicine, and biology as well as for departments of anatomy, histology, embryology; it is also recommended for students of stomatology and for departments or clinics of dermatology.)