A 16-day-old embryo at the stage of the bilaminar germ disc illustrates the development of the notochord as viewed in longitudinal section. The disc is cut longitudinally on the mediosagittal plane, and one half is removed. The following features of the disc are described: epiblast, hypoblast, primitive node, primitive pit with early mesodermal cells, buccopharyngeal and clocal membranes, and allantois. The origin of each structure is marked by a distinct frame. The growth of the notochordal process with the future prechodral plate is animated up to a 17-day-old embryo. The prechordal plate reaches the buccopharyngeal membrane, while the notochordal process shows the dorsal and ventral wall. An approximately 17.5-day-old embryo shows the gradual fusion of the ventral wall of the notochordal process with the underlying endoderm and its degeneration. The cells of the prechordal plate merge with the endoderm. After the degeneration of the ventral wall of the notochordal process, an 18-day-old embryo reveals the formation of the neurenteric canal. During the course of the 19th day, the entire ventral wall of the notochordal process degenerates, so that only its dorsal wall remains; this constitutes the notochordal plate. Between the 19th and 20th day, the definitive notochord detaches from the endoderm in the caudal direction to form the definitive notochord.

The next sequence animates the formation of the definitive notochord in a 20-day-old embryo. During the next day, the lordotic flexure of the 21-day-old embryo is animated in 3D along with the lengthening of the notochord from the buccopharyngeal to the cloacal membranes. At the same time, the notochord induces the formation of the neural plate, while the pericardial cavity, cardiogenic plate and endocardial tubes differentiate in the cardiogenic area. Finally, kyphotic cephalocaudal folding in a 27-day-old embryo replaces the lordotic flexure, and the notochord becomes separated from the endoderm.

The next sequences animate the development of the notochord as viewed in transversal section. The bilaminar disc of a 16-day-old embryo is rotated and sectioned transversally. The growth of the notochordal process from the primitive node is animated along with the future prechordal plate at its tips. The growth of the notochordal process preceded by the prechordal plate is animated in an embryo early in the 17th day. A transversal band of the embryo is cut out and described. The epiderm, mesoderm and endoderm are visible as is the notochordal process. In the next sequence, the cells of the notochordal process mix with the cells of the endoderm to form the notochordal plate. In a 17-day-old embryo, the degeneration of the ventral wall of the notochordal process is shown. The next day, the dorsal wall of the notochordal process becomes incorporated into the endoderm, thus forming the notochordal plate.

In a 19-day-old embryo, the cells of the notochordal plate proliferate and detach from the endoderm to form the definitive notochord. Laterally, the notochord is flanked by the somites and dorsal aortae. The elevation of the embryo and its kyphotic folding are animated. The notochord moves away from the endoderm ventrally to the neural tube, as shown in an approximately 24-day-old embryo.

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