They make up a fraction of the death toll along the border in Texas. In just one county, the bodies and remains of more than 500 migrants have been found since 2009.

More than 200 other migrants just like him died, their names unknown. Their bodies are part of a border-crossers’ morgue at a university lab.

Case 0438 A man illegally crossed the border into South Texas, died on the journey and was never identified. His remains were buried in a milk crate, his skull stained red from its contact with a bandanna.

SAN MARCOS, Tex. — Case 0435 died more than a mile from the nearest road, with an unscuffed MacGregor baseball in his backpack. Case 0469 was found with a bracelet, a simple green ribbon tied in a knot. Case 0519 carried Psalms and Revelation, torn from a Spanish Bible. Case 0377 kept a single grain of rice inside a hollow cross. One side of the grain read Sara, and the other read Rigo.

The belongings are part of a border-crossers’ morgue at a Texas State University lab here — an inventoried collection of more than 2,000 objects and 212 bodies, the vast majority unidentified.

All 212 were undocumented immigrants who died in Texas trying to evade Border Patrol checkpoints by walking across the rugged terrain. Most died from dehydration, heatstroke or hypothermia. Even as the number of people caught trying to illegally enter the United States from Mexico has dropped in recent months, the bodies remain a constant, grim backdrop to the national debate over immigration.

“When we get them, we assign them a case number because we have to have a way of tracking cases, but no one deserves to be just a number,” said Timothy P. Gocha, a forensic anthropologist with Operation Identification, a project at Texas State University’s Forensic Anthropology Center that analyzes the remains and personal items of the immigrants to help identify them. “The idea is to figure out who they are, and give them their name back.”

The collection in San Marcos represents only a fraction of the total deaths. Hundreds of immigrants have died crossing the border in Texas in recent years, and hundreds of others have died in the three other states that share a border with Mexico — Arizona, California and New Mexico.

In South Texas, the number of deaths has overwhelmed some local officials and made the grisly discovery of decomposing bodies a commonplace occurrence. The body count since 2014 stands at nine at one ranch, 17 at another and 31 at a third. A former governor of Texas, Mark W. White Jr., called the authorities in 2014 after he found part of a human skull on a quail-hunting trip near a Border Patrol checkpoint.

“It was an awful thing,” said Mr. White, 77. “The first question that was asked of us was, ‘Is the body fresh?’ The lady who was answering the call said, ‘We can’t pick him up today because we have three fresh ones we have to pick up today.’”

‘A Mass Disaster’

FALFURRIAS, Tex. — The sheriff and his deputies here call it a Code 500: a report of a deceased person. There have been so many in rural Brooks County that the case files fill more than a dozen thick binders.

The bodies and remains of more than 550 undocumented migrants have been discovered in Brooks County since January 2009. Those bodies were only those reported to the authorities.

“I would say for every one we find, we’re probably missing five,” said Sheriff Urbino Martinez, adding that the scale of the problem often gets overlooked “because it doesn’t happen all in one bulk. It’s spread out through months, years.”

150 129 bodies 120 The number of bodies recovered in the first months of 2017 already nearly equals all of 2010. 90 60 30 0 2009 2010 2011 2012 2013 2014 2015 2016 As of April 2017 150 129 bodies The number of bodies recovered in the first months of 2017 already nearly equals all of 2010. 120 90 60 30 0 2009 2010 2011 2012 2013 2014 2015 2016 As of April 2017 150 129 bodies The number of bodies recovered in the first months of 2017 already nearly equals all of 2010. 120 90 60 30 0 2009 ’10 ’11 ’12 ’13 ’14 ’15 ’16 As of April 2017

More people have died illegally crossing the southwestern border of the United States in the last 16 years than were killed in the Sept. 11, 2001, terrorist attacks and Hurricane Katrina combined. From October 2000 through September 2016, the Border Patrol documented 6,023 deaths in Arizona, California, New Mexico and Texas, while more than 4,800 people died in the Sept. 11 attacks and Hurricane Katrina.

Local officials and immigrant advocates said the frequency of the deaths amounts to a humanitarian crisis. No other Texas county has discovered more migrant bodies than Brooks County. One day in February 2015, deputies found the bodies of four migrants near a lake called Laguna Salada, their skeletal remains spread across a one-mile area. The four people died separately over the span of months. They just happened to be discovered on the same day. But there are other counties where bodies turn up with stunning regularity, in both Texas and Arizona, the two states with the most deaths.

“If this were any other context, if these were deaths as a result of a mass flood or an earthquake or a major plane crash, people would be talking about this as being a mass disaster,” said Daniel E. Martinez, an assistant professor of sociology at George Washington University and the lead author of a Binational Migration Institute report on migrant deaths in Arizona.

Hebbronville checkpoint The remains of more than 75 bodies have been recovered and cataloged by the Brooks County sheriff’s department from 2016 to the present. The Hebbronville and Falfurrias checkpoints create a bottleneck as border-crossers attempt to avoid capture. Falfurrias 60 miles from border Sarita checkpoint Falfurrias checkpoint 50 miles Brooks County United States MEXICO 40 miles TEXAS Each dot represents a recovered body or body part. 30 miles TAMAULIPAS Escobares Rio Grande City Edinburg 15 miles NUEVO LEON Hebbronville checkpoint The remains of more than 75 bodies have been recovered and cataloged by the Brooks County sheriff’s department from 2016 to the present. The Hebbronville and Falfurrias checkpoints create a bottleneck as border-crossers attempt to avoid capture. Falfurrias 60 miles from border Sarita checkpoint Falfurrias checkpoint 50 miles Brooks County United States MEXICO 40 miles TEXAS Each dot represents a recovered body or body part. 30 miles TAMAULIPAS Escobares Rio Grande City Edinburg 15 miles NUEVO LEON The remains of more than 75 bodies have been recovered and cataloged by the Brooks County sheriff’s department from 2016 to the present. The Hebbronville and Falfurrias checkpoints create a bottleneck as border-crossers attempt to avoid capture. Hebbronville checkpoint 60 miles from border Sarita Falfurrias 50 miles Brooks County 40 miles TEXAS 30 miles Each dot represents a recovered body or body part. 15 miles MEXICO

When Vultures Visit

ENCINO, Tex. — Ryan Weatherston was on the way to check a windmill on a ranch here last year. He stopped when he noticed the buzzards.

Mr. Weatherston saw the body of a man in the grass. The man was on his back, his head resting on a tree branch and his right arm touching a water jug. He carried religious beads and a vehicle registration card from El Salvador for a 1979 beige Datsun.

Mr. Weatherston, 35, manages the 8,600-acre ranch in Brooks County. Eight bodies or sets of remains have been found on the ranch in the last five years. Mr. Weatherston recalled the body that appeared to be standing up, because it had been propped up against a tree, and the one they spotted from a helicopter during a game survey.

“It’s not what I signed up for,” he said.

In a harsh yet tranquil landscape of cactus, mesquite trees and sandy cattle trails, a kind of unseen ghastliness plays out along the border. The bodies of immigrants have been eaten and pulled apart by vultures, feral hogs and other creatures. Numerous skulls and craniums analyzed by Texas State University researchers have jagged holes at the back of the eye sockets — vultures punch out the thin bone as they pick at the eyes.

On a recent afternoon, Mr. Weatherston drove to the thick grass where he found the body of the Salvadoran man. The long branch the man’s head rested on was still there. But the gallon water jug, left behind by the authorities, was gone. Mr. Weatherston said he had seen the jug recently. Another migrant walking through most likely found it, and took it.

A Path Lined by the Dead

FALFURRIAS, Tex. — It was about 12:25 p.m. when the body of Isabel Cruz Cueto, 30, was found on a ranch here on June 1, 2016. His head rested on a plaid blanket at the base of a tree. His birth certificate, from Chiapas, Mexico, was folded neatly in his wallet.

Around 4:45 p.m., a second body was reported at another ranch about 13 miles away. Juan Guzman Perez died of hyperthermia, a heat-related illness, as did Mr. Cueto. The two men were far from the border, about 80 miles north of it. They had separately crossed the border but died in Brooks County trying to circumvent a lesser-known layer of border security: the Border Patrol’s inland checkpoints.

The traffic checkpoints are spread out along border counties in Arizona, California, New Mexico and Texas. They are not on the borderline but up to 100 miles north, like the one near Falfurrias on Highway 281.

“Brooks County is a choke point,” said Don White, a reserve sheriff’s deputy who has recovered numerous bodies. “You either go up the highway or you walk across the ranches. That’s it.”

The dead line the way. In March, immigrants came upon scattered bones as they hiked through a ranch. They picked up the bones, assembled the stranger’s skeleton and continued on.

The migrants are in perpetual transit. They pay guides known as coyotes who escort them across the Rio Grande into Texas and crowd them into stash houses near the border. Then they are driven to remote areas closer to the checkpoints and dropped off to begin their trek on foot. Some are ready for a long hike, with backpacks and energy drinks, but many carry very little. Last January, a woman who died of dehydration and hypothermia was found wearing a trash bag to stay warm and dry.

After the migrants die, they travel once more. With a population of 7,200, Brooks County lacks a coroner, so many of the bodies are driven to Laredo, in Webb County, a two-hour, 100-mile trip. Dr. Corinne E. Stern, the chief medical examiner of Webb County, has examined 171 migrants since 2016, including Mr. Cueto and Mr. Perez.

Dr. Stern keeps a frayed sign of a Latin phrase in her office above the receptionist’s window: Mortui Vivis Praecipant.

Let the dead teach the living.

Milk Crates as Coffins

FALFURRIAS, Tex. — Forensic anthropologists and college students were digging at Sacred Heart cemetery here in May 2013 when they noticed something unusual: the outline of a coffin that was smaller than any others.

Researchers from the University of Indianapolis, Baylor University and Texas State University have exhumed dozens of graves of unidentified immigrants at Sacred Heart to analyze the bodies and help determine their identities.

The team from the University of Indianapolis realized the outline was not a coffin at all. It was a milk crate.

Someone had buried an unidentified migrant in a milk crate and wrapped it in a red biohazard bag. Inside the lidless crate were skeletal remains — a cranium, ribs and other bones — and a red bandanna.

The discovery of the milk crate hinted at a larger problem. For years, the process of examining and burying unidentified migrants was mishandled along the Texas border. Bodies were buried in clusters of up to five. And many were buried either without DNA samples being taken or without any samples being submitted to a state DNA database, as required by Texas law. The situation has steadily improved, but immigrant advocates and forensic anthropologists continue to be concerned about the way officials in rural border counties handle migrant burials.

At Sacred Heart cemetery, 145 unidentified immigrants were exhumed in 2013, 2014 and 2017. Of those 145, 41 were buried in some sort of grouping. At one grave site, a single coffin contained the remains of five individuals, each buried in a biohazard bag or body bag.

“It’s telling us a little bit about the results of our Border Patrol policies, where we’re funneling individuals into areas that are very dangerous for them to try to survive, and as an end result, overwhelming counties that can’t deal with the situation,” said Krista E. Latham, the director of the University of Indianapolis Human Identification Center and an associate professor of biology and anthropology, who led the university’s Texas exhumations.

In 2014, the Texas Rangers looked into whether state laws had been broken at Sacred Heart. The Rangers concluded that there was insufficient evidence to open a criminal investigation. There are no Texas laws prohibiting one set of human remains from being buried with other bodies in the same grave or coffin. And as defined by Texas health laws, a coffin is any container used to hold the remains of a deceased person.

Service Corporation International, the parent company of Funeraria del Angel Howard-Williams, which handles migrant burials, said in a statement that it had fully cooperated with the Rangers inquiry, which “concluded there was nothing unlawful or inappropriate” about the funeral home’s work on behalf of Brooks County.

The remains in the milk crate were eventually sent to Texas State University. Over time, the cranium’s contact with the red bandanna caused the dye to seep onto the bones.

It left a stain across the face of Case 0438.

Lost and Seeking a Lifeline

CARRIZO SPRINGS, Tex. — Monica M. Espinoza was struck by the man’s name: Francisco. Just like her brother.

Ms. Espinoza works as a dispatch supervisor for Sheriff Marion Boyd of Dimmit County. She and other dispatchers have handled hundreds of calls from immigrants who get lost in the brush and dial 911 after wandering for days. By the time they call, many are desperate, dehydrated and eager to be apprehended to save their lives. The sheriff’s office received 501 calls from lost migrants from 2011 to 2016.

It was a September morning in 2015 when Francisco — his full name was Francisco Gonzalez — called 911, asking for help.

Ms. Espinoza stayed on the phone with him for more than two hours. Mr. Gonzalez, 32, had crossed the border with a group of migrants. They scattered through the brush after being chased by Border Patrol agents. Mr. Gonzalez hid, but became lost.

The dispatchers and deputies were unable to find him. At one point, the deputies turned their sirens on, and Ms. Espinoza asked Mr. Gonzalez in Spanish if he heard any sirens.

“Nada,” he told her.

The Border Patrol joined the search, but Mr. Gonzalez was never found. Near the end of his call, Mr. Gonzalez pleaded with Ms. Espinoza to call his fiancée in Houston. “He gave me her phone number,” Ms. Espinoza said. “He kept telling me, ‘Call her and tell her I didn’t make it. Call her and tell her I love her and for her to take care of our baby.’”

The baby, a girl, was 3 months old at the time. Mr. Gonzalez had never seen her as a free man. He had been incarcerated when she was born.

Mr. Gonzalez was a machinist from Tamaulipas, Mexico. He had illegally crossed the border several times and had been living in Houston, where he met his fiancée, 27, who asked to be identified by her middle name of Esmeralda. He was arrested on drunken-driving charges in Houston, detained by the immigration authorities and deported to Mexico. He was making his second attempt to cross the border in three months when he became lost.

Without Mr. Gonzalez’s body, Esmeralda knew of only one way to find closure. She asked a lawyer, Ryan W. Smith, to get a copy of the 911 recording. “I wanted to have something of him, to have his last conversation,” Esmeralda said.

She has listened to the CD four times. Years from now, when their daughter is older, Esmeralda plans to play it for her, too.