To hold off for jugular vein you hold the jugular vein off at the thoracic inlet by pressing down firmly in the thoracic inlet, which is the groove at the base of the neck, just above the breastbone.
Place your thumb or fingers deep into the thoracic inlet, "jugular groove/furrow" on the same side you're drawing blood from.
Apply firm, and consistent pressure in an upward and slightly inward direction to block flow and make the vein "pop" or stand up.
And ensure that the head is also extended upward and slightly away from the side that is being drawn, which also stretches the neck and also helps the vein fill up.
If you can't feel it, have the holder move the head slightly until the vessel does become palpable.
The thoracic inlet (cranial aperture) in animals is the narrow opening at the top of the thoracic cavity, bounded by the first thoracic vertebra, the first pair of ribs, and the manubrium of the sternum.
The thoracic inlet in animals acts as a vital conduit for structures moving between the neck and chest, including the trachea, esophagus, and major blood vessels (jugular veins, carotid arteries).
Formed by the first pair of ribs laterally, the first thoracic vertebra (\(T_{1}\)) dorsally, and the cranial edge of the sternum (manubrium) ventrally.
It also contains the trachea, esophagus, vagus nerves, phrenic nerves, recurrent laryngeal nerves, and major vessels like the trachea, esophagus, great arteries and veins.
The thoracic inlet is oval-shaped and oriented obliquely in most domestic animals.
In dogs, the thoracic inlet is a key reference point for radiographic heart size.