Human lower jaw viewed from the left

The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of most animals.

Arthropods[link]

The mandibles of a Bull ant

In arthropods, the jaws are chitinous and oppose laterally, and may consist of mandibles or chelicerae. These jaws are often composed of numerous mouthparts. Their function is fundamentally for food acquisition, conveyance to the mouth, and/or initial processing (mastication or chewing). Many mouthparts and associate structures (such as pedipalps) are modified legs.

Vertebrates[link]

In most vertebrates, the jaws are bony or cartilaginous and oppose vertically, comprising an upper jaw and a lower jaw. The vertebrate jaw is derived from the most anterior two pharyngeal arches supporting the gills, and usually bears numerous teeth.

Jaws of great white shark

The jaw in fish[link]

Moray eels have two sets of jaws: the oral jaws that capture prey and the pharyngeal jaws that advance into the mouth and move prey from the oral jaws to the esophagus for swallowing

The vertebrate jaw probably originally evolved in the Silurian period and appeared in the Placoderm fish which further diversified in the Devonian. The two most anterior pharyngeal arches are thought to have become the jaw itself and the hyoid arch, respectively. The hyoid system suspends the jaw from the braincase of the skull, permitting great mobility of the jaws. While there is no fossil evidence directly to support this theory, it makes sense in light of the numbers of pharyngeal arches that are visible in extant jawed vertebrates (the Gnathostomes), which have seven arches, and primitive jawless vertebrates (the Agnatha), which have nine.

It is thought that the original selective advantage garnered by the jaw was not related to feeding, but to increased respiration efficiency. The jaws were used in the buccal pump (observable in modern fish and amphibians) that pumps water across the gills of fish or air into the lungs in the case of amphibians. Over evolutionary time the more familiar use of jaws (to humans), in feeding, was selected for and became a very important function in vertebrates. Many teleost fish have substantially modified their jaws for suction feeding and jaw protrusion, resulting in highly complex jaws with dozens of bones involved.

The jaw in amphibians, reptiles, and birds[link]

The jaw in tetrapods is substantially simplified compared to fish. Most of the upper jaw bones (premaxilla, maxilla, jugal, quadratojugal, and quadrate) have been fused to the braincase, while the lower jaw bones (dentary, splenial, angular, surangular, and articular) have been fused together into a unit called the mandible. The jaw articulates via a hinge joint between the quadrate and articular. The jaws of tetrapods exhibit varying degrees of mobility between jaw bones. Some species have jaw bones completely fused, while others may have joints allowing for mobility of the dentary, quadrate, or maxilla. The snake skull shows the greatest degree of cranial kinesis, in order to allow the snake to swallow large prey items.

The jaw in mammals[link]

In the evolution of the mammalian jaw, two of the bones of the jaw structure (the articular bone of the lower jaw, and quadrate) were reduced in size and incorporated into the ear, while many others have been fused together.^[1] As a result, mammals show little or no cranial kinesis, and the mandible is attached to the temporal bone by the temporomandibular joint. Temporomandibular joint disorder is a common disorder of this joint^{[citation needed]}, and can cause pain and loss of joint mobility.

Sea urchin jaws[link]

Sea urchins possess unique jaws which display 5-part symmetry, termed the "Aristotle's lantern". Each unit of the jaw holds a single, perpetually-growing tooth composed of crystalline calcium carbonate.

See also[link]

• Tooth
• Gnathostomata - jawed vertebrates
• Muscles of mastication
• Otofacial syndrome
• Predentary
• Premaxilla
• Prognathism
• Rostral bone

References[link]

External links[link]

Look up jaw in Wiktionary, the free dictionary.

• Prehistoric Fish Had Most Powerful Jaws
• Jaw at the US National Library of Medicine Medical Subject Headings (MeSH)

Jason Heyward
Heyward at spring training in February, 2011
Atlanta Braves – No. 22
Right fielder
Born: (1989-08-09) August 9, 1989 (age 22) Ridgewood, New Jersey
Bats: Left	Throws: Left
MLB debut
April 5, 2010 for the Atlanta Braves
Career statistics (through May 8, 2012)
Batting average	.257
Home runs	36
Runs batted in	127
Stolen bases	29
Teams
Atlanta Braves (2010–present)
Career highlights and awards
All-Star selection (2010) 2x MLB Rookie of the Month Award (April and May, 2010) Hit a home run in his first at bat in each of the first two years of his career. Baseball America Rookie of the Year: 2010. The Sporting News Rookie of the Year Award NL 2010

Jason Alias Heyward^[1] (born August 9, 1989 in Ridgewood, New Jersey), nicknamed J-Hey and J-Hey-Kid, is a Major League Baseball right fielder for the Atlanta Braves. He throws and bats left-handed.

Heyward was considered the consensus number one Major League Baseball prospect for the 2010 season. Baseball America, Keith Law of ESPN.com and Jonathan Mayo of MLB.com all listed Heyward as baseball's top prospect in 2010 season previews.^[2] In 2007, he was regarded as the top prospect in the Braves minor league system, according to Baseball America,^[3] being listed by the publication as the organization's best power hitter and having the best strike zone discipline in the system.

Amateur career[link]

Heyward was born in Ridgewood, New Jersey but moved to Georgia soon after he was born.^[4] Heyward went to Henry County High School. He was selected 14th overall by Atlanta in the 2007 Major League Baseball Draft, and signed a deal worth $1.7 million – $170,000 more than MLB's slot recommendation of $1.53 million, and the same as the 2006 14th-slot amount that the Toronto Blue Jays gave Travis Snider on August 12, 2007.^[5][6]

Professional career[link]

At 17, Heyward started his professional career for the Braves, first with the GCL Braves and then with the Danville Braves of the Appalachian League, hitting a combined .302 batting average with one home run and six RBIs in 12 games. In 2008 he hit a combined .316 with 11 home runs and 52 RBIs in 127 games for Class-A Rome and Advanced-A Myrtle Beach, including 91 runs, 15 stolen bases, and a .854 OPS.

Heyward started 2009 at Myrtle Beach, gaining successive promotions to Double-A Mississippi and Triple-A Gwinnett. In 99 games, he was a .323 hitter with 17 homers and 10 steals, including high numbers in OBP (.408), SLG (.555), and OPS (.963), while scoring 69 runs and driving in 63 RBIs.

In September 2009, Heyward was named the Minor League Player of the Year both by Baseball America and USA Today.^[7]

During Spring Training in March 2010, Heyward hit two notable batting practice home runs. One hit and damaged a Coca-Cola truck in the parking lot, and another broke the sunroof of Atlanta Braves' assistant GM Bruce Manno's car in the same lot.

Major leagues[link]

2010[link]

On March 25, 2010, he was named the Braves' starting right fielder. Heyward wears #22 in honor of a deceased high school teammate and friend, Andy Wilmot.^[8]

On April 5, during his first Major League plate appearance, Heyward hit a three-run home run, estimated at 471 feet (144 m), off of Carlos Zambrano of the Chicago Cubs.^[9] Heyward became the fifth player in Braves history to hit a home run in his first Major League at bat, on the heels of Jordan Schafer, who did it the previous year.

He was named Rookie of the Month in April ^[10] and May^[11] of 2010.

Heyward was selected as a starter for the 2010 All-Star Game, but did not play due to an injury to his right thumb. On July 28, Heyward stole home on a double steal against the Washington Nationals, the first Brave to steal home since Rafael Furcal, who did it more than ten years earlier. On August 22, against the Chicago Cubs, Heyward had his first career multi-home run game and set a career high in hits and runs scored with four. He made his post-season debut with the Braves on October 7, 2010 against the San Francisco Giants.

Heyward finished his rookie season with a .277 batting average, a .393 on-base percentage, and 18 home runs.^[12] He was named an outfielder on Baseball America's 2010 All-Rookie Team.^[13] He was also named an outfielder on the 2010 Topps Major League Rookie All-Star Team.^[14] Heyward finished second in the Rookie of the Year voting to Buster Posey.

2011[link]

Heyward again hit a home run in his first at-bat of the season on March 31, 2011 off Washington Nationals pitcher Livan Hernandez to become the second player to homer in his first major league at-bat on opening day, and do the same the following year, after Kazuo Matsui did so 2004-2005.^[15] During a game against the Chicago Cubs on August 23, 2011, Heyward hit his first career grand slam.^[16]

See also[link]

• List of players with a home run in first major league at-bat

References[link]

External links[link]

Wikimedia Commons has media related to: Jason Heyward

• Career statistics and player information from MLB, or ESPN, or Baseball-Reference, or Fangraphs, or The Baseball Cube, or Baseball-Reference (Minors)
• MLB Top 50 prospects – Scouting Report