BL 40  Found at the centre of the popliteal crease, or in the centre of the popliteal fossa.

Needle insertion is from behind anteriorly, parallel with the ground, and the long axis of the dog, and to a depth of up to 25mm in a large dog or 10mm in a small dog.

The popliteal fossa is located behind the knee or stifle of the dog.

When the dog is standing the fossa may not be apparent. To discover the popliteal fossa one needs to lift the hindleg from the ground and cause flexing of the stifle joint.

As you flex and extend the joint with one hand, you should gently poke your free index finger from behind the stifle anteriorly. As the joint flexes, your finger will "fall into" a depression, bounded medially by the tendon of the semitendinosis muscle, and laterally by the biceps femoris muscle.

This depression is the popliteal fossa. The deepest most central point of the fossa is

Explore this fossa with your finger and identify the structures that surround it. Note that the fossa tends to disappear when the leg is extended and placed back on the ground.

The popliteal crease is an imaginary line which joins the lateral and medial sides of the fossa. It is best "visualised" with the stifle flexed.
My Graphic
In practice, one usually finds BL40 in the centre of the depths of the popliteal fossa.

Insertion of the needle is 0.5 - 2.0cm, depending on the size of the dog, parallel to the long axis of the dog and parallel to the ground, towards the centre of the knee joint.

My Graphic