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Carnegie Stage 19 Introduction

Stage 19 embryos have a greatest length of 16 to 18 mm and an estimated postfertilization age of approximately 45 to 47 days. The trunk is elongating and straightening. The head no longer forms a right angle with the back and is beginning to elevate. The hand and footplates contain distinct metacarpal and metatarsal condensations, respectively. The auricular hillocks are no longer evident and have blended forming definitive parts of the external ear. The cochlear duct begins its 2 1/2 turn spiral with the tip turned upward. The mesonephric duct and ureter join close to the urinary bladder and continue to the horn of the bladder as a common excretory duct.

The stage is represented by Carnegie embryo # 9325 that has a grade of good but is considered to be one of the best specimens in the Carnegie collection at this stage. It was recovered in 1955 from a tubal pregnancy, fixed in formol acetic and embedded in paraffin. The corrected greatest length after fixation was 17 mm. The specimen was serially sectioned transverse to the long axis; most sections were cut at 15 microns but in the heart region they were cut thinner (63 @ 8 microns and 42 @ 10 microns). The sections were mounted on 37 large glass slides and stained with azan and silver. There are 980 sections through the embryo.

The Browse part of the DREM database includes 134 of the 980 sections. Approximately every 10th section was digitally restored and labeled, and can be viewed at four magnifications. Several 3D reconstructions were produced from the aligned sections. Animations of the 3D reconstructions of the embryo surface and fly-through animations of the aligned sections are also included on the disks.

Source: The Virtual Human Embryo.