Step 2: The First Incision

Subcutaneous Incision

After checking to see if the mouse is OK on the outside, it is time to see what is wrong (or, depending on your perspective, what is right) with the mouse on the inside.

1. First, pin the animal down with his or her belly facing up. Wet the animal down with ethanol. By washing the carcass with ethanol, not only are you sterilizing the future incision, you are protecting the tissues from artifacts caused by hair dragging through them.
2. With your forceps, grab hold of the skin anterior to the urethral opening. Using your scissors, cut along the ventral midline from the groin to the chin, being careful to  cut only the skin and not the muscle wall underneath. (See diagram for location of incisions)
3. Next, make an incision from the start of the first incision to down near the knee on both sides of the animal. Basically, you will end up with an incision that looks very similar to an upside down Y.
4. Reflect the skin back (retract) on the sides and you are ready for further examination. You can see the underlying organs through the peritoneal wall, as diagramed in the drawing.
5. If the animal is male, the penis and the prepuital gland will lie on top of the muscle. By cutting between the prepuital gland and the muscle wall via the penis, the gland is left intact for preservation.
6. As with any tissue to be kept, place the prepuital gland and the penis in formalin or other fixative of your choice.

Gross Anatomy of Mouse After Peritoneal Wall Incision

Salivary Gland Rib Cage Diaphram Liver Intestines	Bulbourethral Gland Testicle with Epididymis Reflected Subcutaneous Skin Reflected Peritoneal Wall

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