CHICAGO/NEW YORK (Reuters) - Officials in Arkansas are investigating a shipment of 40 to 60 human heads found by Southwest Airlines employees at a cargo facility last week in Little Rock, the Pulaski County coroner said on Thursday.

The shipment of three separate containers was discovered last Wednesday at the facility after employees saw the package was “not labeled properly,” Southwest spokeswoman Ashley Rogers said.

“Although it is common to transport human specimens for medical purposes, a longstanding Southwest cargo customer attempted to transport a shipment without following policies in relation to labeling, packaging, and properly declaring the contents,” the company said in a statement on its website.

Southwest employees opened the box last Wednesday evening, found the heads and contacted local police, who turned the heads over to the local coroner.

“They were basically in plastic containers with lids that are not air-sealed,” Coroner Garland Camper said. “They were duct-taped with minimal information to disclose what was inside.”

The heads were being shipped to a Medtronic Inc facility in Fort Worth, Texas. They were for educational training for neurosurgeons studying ear, nose and throat procedures, said Medtronic spokesman Brian Henry.

Camper said there were between 40 and 60 heads packed in three containers. Henry said the company had ordered four heads and 40 skull parts, or the portion of the head with the ear.

“In this particular instance, they were going to be used for educational training, which is routinely and commonly done,” Henry said.

It is not uncommon for heads used for research and educational training to be shipped commercially, he said.

“It’s a common practice,” Henry said. “This is a very uncommon result.”

Medtronic, the world’s largest independent medical device company, employed Arkansas-based JLS Consulting to supply and ship the head and head parts. Calls and an e-mail to JLS Consulting were not immediately returned.

The 24-hour Southwest cargo facility is one of 70 operated by the low-cost airline and typically handles shipments of items like flowers and seafood, Rogers said.

Camper, the Pulaski Country coroner, said his office took possession of the heads after being contacted by officials in Little Rock.

“Since then we have learned that the paperwork that we have asked for does not quite meet the same description of the specimens that we have,” he said. “So we’ve got some discrepancies there.”

Camper said he wanted to confirm that the heads were not being shipped as part of a black market for human body parts.

“We definitely want to make sure this is not a part of something like that,” he said.