medullary groove n.
See neural groove.
The second (fig. 14) section passes through the medullary groove where it has become wider.
The first traces of it become apparent while the medullary groove is still extremely shallow.
In sections its front end appears as a ridge on one side or on the middle of the floor of the widened end of the medullary groove.
The anterior section (D) passes through the medullary groove near its hinder end.
I pointed out that beneath the medullary groove the epiblast and hypoblast were not separated by any interposed mesoblast.
The remains of the primitive streak (pr) are still present behind the medullary groove.
No trace of a medullary groove is to be met with in the head, which simply consists of a wide flattened plate.
The medullary groove becomes closed for its whole length with the exception of a small posterior portion.
This plate is the medullary plate; along its axial line is a shallow groove—the medullary groove (mg).
At about the time of the formation of the medullary groove, the mesoblast becomes definitely constituted.