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Carnegie Stage 1 - First Trimester
A Four Chambered Heart




SIZE: 10.0 - 13.0 mm

TIME PERIOD: 42 - 44 days post-ovulation


Head and Neck
Jaw and facial muscles are now developing. The nasofrontal groove becomes distinct and an olfactory bulb (sense of smell) forms in the brain. Auricular (ear) hillocks become recognizable. The dental laminae or teeth buds begin to form.

The pituitary, which is the master gland responsible for growth of hormones that regulate other glands, such as the thyroid, adrenal glands, gonad) begins to form.Trachea, the larynx and the bronchi begin to form.

Thorax
The heart begins to separate into four chambers. Diaphragm, the tissue that separates the chest cavity from the abdomen, forms.

Abdomen
Intestines begin to develop within the umbilical cord and will later migrate into the abdomen when the embryo's body is large enough to accommodate them.

Pelvis
Primitive germ cells arrive at the genital area and will respond to genetic instructions to develop into either female or male genitals.

Limbs
Hand region of upper limb bud differentiates further to form a central carpal part and a digital plate. The thigh (rostrolateral part), leg (the caudomedial part) and foot areas can be distinguished in the lower limb buds.
Digital rays in appear in the foot plates and finger rays are more distinct.

Spine
Trunk becomes straighter.

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