Developmental Anatomy
Stage 19: Summary
External: The trunk has begun to elongate and straighten slightly, with the result that the head no longer forms a right angle with the line of the back of the embryo. The limbs extend nearly directly forward; The toe rays are more prominent, but interdigital notches have not yet appeared in the rim of the foot plate. all four limb buds are usually visible; the optic vesicle is closed; the lens disc is generally not yet indented.
Internal: Septum primum and foramen primum appear in the heart; right and left lung buds are recognizable, and the trachea begins its development; retinal and lens discs appear; the endolymphatic appendage becomes distinguishable by the end of the stage.
Lab Manual - Horizon 19 (CC#4501)
- Length 17 - 20 mm.
- Trunk beginning to straighten out and cervical angle less acute.
- Coalescence of parts of branch region has altered appearances of external ear, and the hillocks are less conspicuous.
- Axes of arm are almost at right angles to the dorsal line of the body of the embryo.
- Various parts in leg and arm can be identified.
- Toe rays are more prominent.
- Ovulation age: 48 - 51 days.
Developmental Stages in Human Embryos by Ronan O'Rahilly and Fabiola Müller.
Published by Carnegie Institution of Washington, Publication 637. 1987.
Stage 19 (PDF 1.5 MB)
QUESTION: What has altered the appearance of the external ear?
