Coracoid

A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (which is to say marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is not homologous with the coracoid bone of most other animals.[1]

In other tetrapods it joins the scapula to the front end of the sternum and has a notch on the dorsal surface which, along with a similar notch on the ventral surface of the scapula, forms the socket in which the proximal end of the humerus (upper arm bone) is located. The acrocoracoid process is an expansion adjacent to this contact surface, to which the shoulderward end of the biceps brachii muscle attaches in these animals. In birds (and generally theropods and related animals), the entire unit is rigid and called scapulocoracoid. This plays a major role in bird flight. In dinosaurs the main bones of the pectoral girdle were the scapula (shoulder blade) and the coracoid, both of which directly articulated with the clavicle.[2]

In fish it provides the base for the pectoral fin.[3]

Monotremes, as well as the extinct therapsids, possess both the coracoid bone of reptiles (here referred to as the procoracoid, or anterior coracoid), and the coracoid process of other mammals, with the latter being present as a separate bone.[1]

Wing Muscles, color
Diagram of skeletal structure and musculature of a bird's wing

See also

Notes

  1. ^ a b Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 186–187. ISBN 0-03-910284-X.
  2. ^ Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300. ISBN 1-4051-3413-5.
  3. ^ FishBase 2006

References

Abavornis

Abavornis is the name given to a genus of primitive birds from the Late Cretaceous, containing the single species A. bonaparti (named in honor of the Argentine paleontologist José Bonaparte). It was probably a member of the Enantiornithes, but as it is only known from a single broken coracoid (TsNIGRI 56/11915), which, however, looks typically enantiornithine, that assignment is tentative. The fossil is from Late Cretaceous Bissekty Formation (Coniacian, 89–86 MYA) in the Kyzylkum, Uzbekistan. Another partial coracoid (PO 4605) is very similar and is referred to as Abavornis sp.; it might belong to A. bonaparti and if so show some features which are damaged in the holotype.

Acromioclavicular joint

The acromioclavicular joint, or AC joint, is a joint at the top of the shoulder. It is the junction between the acromion (part of the scapula that forms the highest point of the shoulder) and the clavicle. It is a plane synovial joint.

Acromion

In human anatomy, the acromion (from Greek: akros, "highest", ōmos, "shoulder", plural: acromia) is a bony process on the scapula (shoulder blade). Together with the coracoid process it extends laterally over the shoulder joint. The acromion is a continuation of the scapular spine, and hooks over anteriorly. It articulates with the clavicle (collar bone) to form the acromioclavicular joint.

Austriadraco

Austriadraco is a genus of pterosaur living during the Late Triassic in the area of present Austria. Its only species—Austriadraco dallavecchiai—was previously attributed to Eudimorphodon, and its closest relatives may have been Eudimorphodon or Arcticodactylus.In June 1994, near Seefeld in Austrian Tirol, at a 1600 metres high mountain trail to the Reither Spitze, in the vicinity of the Reither Joch-Alm, Bernd Lammerer discovered a pterosaur skeleton. The remains have been secured as five stone plates, removed on several occasions. In 2003, Peter Wellnhofer identified the fossil as a specimen of Eudimorphodon, a cf. E. ranzii. As it was 10 to 25% shorter than the latter's holotype, Wellnhofer considered it a juvenile. The same year Fabio Marco Dalla Vecchia doubted the comparability to E. ranzii and suggested that it represent a separate Eudimorphodon species. In 2009, Dalla Vecchia concluded that the specimen was neither a juvenile nor closely related to Eudimorphodon.In 2015, Alexander Kellner named the separate genus Austriadraco, with the type species Austriadraco dallavecchiai. The generic name is a combination of the Latin words Austria and draco, "dragon". The specific name honours Dalla Vecchia. The Life Science Identifiers are for the genus 120B3003-6DE3-41B4-AF6B-6F242FB2A777 and for the species 6E123721-07EA-419CB755-9981CC7D9209.The holotype, BSP 1994 I 51, was found in a layer of the Seefeld Formation, dating from the late Norian. It consists of a partial and disarticulated skeleton with skull. It contains both frontal bones, a left jugal, the lower jaws, loose teeth, vertebrae of the neck, back and tail, the shoulder girdle, both humeri, a first wing phalanx, the pelvis, a shinbone and a calf bone. The fused frontals had in 2003 been incorrectly identified as a breast bone by Wellnhofer. The bones have been partly preserved as impressions only and many are fragmented. The fossil is part of the collection of the Bayerische Staatssammlung für Paläontologie und historische Geologie at Munich.Austriadraco dallavecchiai is a small species. Humerus length is about four centimetres. In 2015 Kellner indicated several distinguishing traits. Some of these are autapomorphies. The frontal bone has a short front branch. The jugal bone has short branches to the front, in the direction of the maxilla and the nasal bone, and a long narrow upwards branch running towards the postorbital bone. In the outer rear side of the lower jaw an opening is present, the mandibular fenestra. The coronoid process of the surangular bone is low. The shoulder blade is considerably longer, 62%, than the coracoid.Additionally, a unique combination of in themselves not unique traits is present. The coracoid is broad, with a constricted shaft. In the pelvis, the ischipubic plate, the fusion of the pubic bone with the ischium, is deep. The shinbone is relatively long, with a length of 57.7 millimetres attaining 70% of the length of the humerus and 92% of the length of the first phalanx of the (fourth) wingfinger.According to Dalla Vecchia's analysis, Austriadraco would have a very basal position in the Pterosauria. Kellner concluded that its affinities were uncertain and placed Austriadraco in a separate, undefined, Austriadraconidae. He suggested a close relationship with Arcticodactylus as both taxa shared the trait of a short coracoid.

Clavipectoral fascia

The clavipectoral fascia (costocoracoid membrane; coracoclavicular fascia) is a strong fascia situated under cover of the clavicular portion of the pectoralis major.

It occupies the interval between the pectoralis minor and subclavius, and protects the axillary vein and artery, and axillary nerve.

Traced upward, it splits to enclose the subclavius, and its two layers are attached to the clavicle, one in front of and the other behind the muscle; the latter layer fuses with the deep cervical fascia and with the sheath of the axillary vessels.

Medially, it blends with the fascia covering the first two intercostal spaces, and is attached also to the first rib medial to the origin of the subclavius.

Laterally, it is very thick and dense, and is attached to the coracoid process.

The portion extending from the first rib to the coracoid process is often whiter and denser than the rest, and is sometimes called the costocoracoid membrane.

Below this it is thin, and at the upper border of the pectoralis minor it splits into two layers to invest the muscle; from the lower border of the pectoralis minor it is continued downward to join the axillary fascia, and lateralward to join the fascia over the short head of the biceps brachii.

The coracoclavicular fascia is pierced by the cephalic vein, thoracoacromial artery and vein, lymphatics and lateral pectoral nerve.

Coracoacromial ligament

The coracoacromial ligament is a strong triangular band, extending between the coracoid process and the acromion.

It is attached, by its apex, to the summit of the acromion just in front of the articular surface for the clavicle; and by its broad base to the whole length of the lateral border of the coracoid process.

This ligament, together with the coracoid process and the acromion, forms a vault for the protection of the head of the humerus.

It is in relation, above, with the clavicle and under surface of the deltoid muscle; below, with the tendon of the supraspinatus, a bursa being interposed.

Its lateral border is continuous with a dense lamina that passes beneath the deltoid upon the tendons of the supraspinatus and infraspinatus.

The ligament is sometimes described as consisting of two marginal bands and a thinner intervening portion, the two bands being attached respectively to the apex and the base of the coracoid process, and joining together at the acromion.

When the pectoralis minor is inserted, as occasionally is the case, into the capsule of the shoulder-joint instead of into the coracoid process, it passes between these two bands, and the intervening portion of the ligament is then deficient.

Coracobrachialis muscle

The coracobrachialis is the smallest of the three muscles that attach to the coracoid process of the scapula. (The other two muscles are pectoralis minor and the short head of the biceps brachii.) It is situated at the upper and medial part of the arm.

Coracoclavicular ligament

The coracoclavicular ligament serves to connect the clavicle with the coracoid process of the scapula.

It does not properly belong to the acromioclavicular (AC) joint articulation, but is usually described with it, since it forms a most efficient means of retaining the clavicle in contact with the acromion. It consists of two fasciculi, the trapezoid ligament in front, and the conoid ligament behind. There is very little movement at the AC joint.

These ligaments are in relation, in front, with the subclavius and deltoideus; behind, with the trapezius. The coracoclavicular ligament is the strongest stabilizer of the AC joint. This ligament is very important in the transmission of weight of the upper limb to the axial skeleton.

Coracohumeral ligament

The coracohumeral ligament is a broad ligament which strengthens the upper part of the capsule of the shoulder joint.

It arises from the lateral border of the coracoid process, and passes obliquely downwards and laterally to the front of the greater tubercle of the humerus, blending with the tendon of the supraspinatus muscle. It has two bands, anterior and posterior, that insert into the lesser and greater tuberosities of the humerus respectively.

This ligament is intimately united to the capsule by its posterior and lower border, but its anterior and upper border presents a free edge, which overlaps the capsule.

Coracoid process

The coracoid process (from Greek κόραξ, raven) is a small hook-like structure on the lateral edge of the superior anterior portion of the scapula (hence: coracoid, or "like a raven's beak"). Pointing laterally forward, it, together with the acromion, serves to stabilize the shoulder joint. It is palpable in the deltopectoral groove between the deltoid and pectoralis major muscles.

Halazhaisuchus

Halazhaisuchus is an extinct genus of archosauriform from the Early Triassic of China. It is known from a single species, Halazhaisuchus qiaoensis, which was named in 1982 from the lower Ermaying Formation in Shaanxi. It was assigned to the family Euparkeriidae as a close relative of the genus Euparkeria from South Africa. Halazhaisuchus is known from a single holotype specimen called V6027, which was discovered in 1977 and includes a portion of the vertebral column, some ribs, two scapulae and two humeri, the right radius and ulna, and a left coracoid. Two rows of plate-like bones called osteoderms run along the length of the vertebrae. When it was first described in 1982, Halazhaisuchus was considered a close relative of Euparkeria because it has primitive features like small intercentra bones between the vertebrae and a large coracoid, not seen in later archosaurs. However, these features are common to many early archosauriforms and are not unique to Euparkeriidae.The fauna of the lower Ermaying Formation closely resemble those of the Cynognathus Assemblage Zone in South Africa. Halazhaisuchus is similar to Euparkeria, while the Chinese Parakannemeyeria and Guchengosuchus resemble the South African Kannemeyeria and Erythrosuchus, respectively.

Lance Formation

The Lance (Creek) Formation is a division of Late Cretaceous (dating to about 69 - 66 Ma) rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the latest Mesozoic vertebrate faunas. The Lance Formation is Late Maastrichtian in age (Lancian land mammal age), and shares much fauna with the Hell Creek Formation of Montana and North Dakota, the Frenchman Formation of southwest Saskatchewan, and the lower part of the Scollard Formation of Alberta.

The Lance Formation occurs above the Baculites clinolobatus ammonite marine zone in Wyoming, the top of which has been dated to about 69 million years ago, and extends to the K-Pg boundary, 66 million years ago. However, the characteristic land vertebrate fauna of the Lancian age (which take its name from this formation) is only found in the upper strata of the Lance, roughly corresponding to the thinner equivalent formations such as the Hell Creek Formation, the base of which has been estimated at 66.8 million years old.

Pangalliformes

Pangalliformes is the scientific name of a provisional clade of birds within the group Galloanserae. It is defined as all birds more closely related to chickens than to ducks, and includes all modern chickens, turkeys, pheasants, and megapodes, as well as extinct species that do not fall within the crown group Galliformes.

A few fragmentary fossils have been described as pangalliforms from the Late Cretaceous (85 million years ago), most notably those of Austinornis lentus. Formerly referred to as Ichthyornis lentus, Graculavus lentus, or Pedioecetes lentus, its partial left tarsometatarsus was found in the Late Cretaceous Austin Chalk near Fort McKinney, Texas. This bird was quite certainly closely related to Galliformes, but whether it was a part of these or belongs elsewhere in the little-known galliform branch of Galloanserae is not clear. In 2004, Clarke classified it within Pangalliformes rather than true Galliformes, pending further fossil finds. Another specimen, PVPH 237, from the Late Cretaceous Portezuelo Formation (Turonian-Coniacian, about 90 Ma) in the Sierra de Portezuelo (Argentina) has also been suggested to be an early relative of true galliformes. This is a partial coracoid of a neornithine bird, which in its general shape and particularly the wide and deep attachment for the muscle joining the coracoid and the humerus bone resembles the more basal lineages of galliforms.Additional galliform-like pangalliformes are represented by extinct families from the Paleogene, namely the Gallinuloididae, Paraortygidae and Quercymegapodiidae. In the early Cenozoic, some additional birds may or may not be early Galliformes, though even if they are, it is rather unlikely that these belong to extant families:

†Argillipes (London Clay Early Eocene of England)

†Coturnipes (Early Eocene of England, and Virginia, USA?)

†Paleophasianus (Willwood Early Eocene of Bighorn County, USA)

†Percolinus (London Clay Early Eocene of England)

†"Palaeorallus" alienus (middle Oligocene of Tatal-Gol, Mongolia)

†Anisolornis (Santa Cruz Middle Miocene of Karaihen, Argentina)More recently, it has been discovered that Sylviornis and its sister taxa, Megavitiornis, lay outside the Galliformes crown group. This same study also presents Dromornithidae as possibly closer to Galliformes than to Anseriformes as traditionally expected, though it acknowledges more work to be needed in this field.

Plesiopleurodon

Plesiopleurodon is an extinct genus of plesiosauroid from the Late Cretaceous of North America. It was named by Carpenter based upon a complete skull and lower jaws, neck vertebrae, and a right coracoid. It was collected from the Belle Fourche Shale (lower Cenomanian), in the Rattlesnake Hills of Wyoming. In naming the specimen, Carpenter (1996, p. 264) noted "Of all known pliosaurs, Plesiopleurodon wellesi most closely resembles Liopleurodon ferox from the Oxfordian of Europe, hence the generic reference."

The species is characterized by a moderately long symphysis bearing 8 pairs of teeth, teeth that are nearly circular in cross-section and which are smooth on the outer surface (except near the base), ribs of the neck vertebrae being singled-headed (double-headed in Jurassic pliosaurs), and a long slender interpectoral bar on the coracoid.

Ruehleia

Ruehleia is a genus of sauropodomorph dinosaur from the Late Triassic period of Germany. The type species is R. bedheimensis, described by Galton in 2001, and is named for the German paleontologist Hugo Ruehle von Lilienstern. The fossils consist of one nearly complete skeleton, consisting of cervical (neck), dorsal (back), and caudal (tail) vertebrae; a partial sacrum; a scapula-coracoid; pelvic bones; most of the limb bones; and partially complete manus (hands).

The fossils were found in central Germany and date to the Norian stage, around 216 to 203 million years ago.

Scapula

In anatomy, the scapula (plural scapulae or scapulas), also known as shoulder bone, shoulder blade, wing bone or blade bone, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones the scapulae are paired, with the scapula on either side of the body being roughly a mirror image of the other. The name derives from early Roman times when it was thought that the bone resembled a trowel or small shovel.

In compound terms, the prefix omo- is used for the shoulder blade in Latin medical terminology. The prefix is derived from ὦμος (ōmos), the Ancient Greek word for shoulder, and is cognate with the Latin (h)umerus.

The scapula forms the back of the shoulder girdle. In humans, it is a flat bone, roughly triangular in shape, placed on a posterolateral aspect of the thoracic cage.

Scapulocoracoid

The scapulocoracoid is the unit of the pectoral girdle that contains the coracoid and scapula.

The coracoid itself is a beak-shaped bone that is commonly found in most vertebrates with a few exceptions.

The scapula is commonly known as the shoulder blade. The humerus is linked to the body via the scapula, the clavicle is connected to the sternum via the scapula as well.

Note: Therian mammals lack a scapulocoracoid.

Suprascapular notch

The suprascapular notch (or scapular notch) is a notch in the superior border of the scapula, just medial to the base of the coracoid process.

This notch is converted into a foramen by the superior transverse scapular ligament, and serves for the passage of the suprascapular nerve (but not its corresponding artery); sometimes the ligament is ossified. The suprascapular artery travels superiorly to the superior transverse ligament.According to Rengachary et al. 1979, there are six basic types of scapular notch:

Type I (8%): Notch is absent. The superior border forms a wide depression from the medial angle to the coracoid process.

Type II (31%): Notch is a blunted V-shape occupying the middle third of the superior border.

Type III (48%): Notch is U-shaped with nearly parallel margins.

Type IV (3%): Notch is V-shaped and very small. A shallow groove is frequently formed for the suprascapular nerve adjacent to the notch.

Type V (6%): Notch is minimal and U-shaped with a partially ossified ligament.

Type VI (4%): Notch is a foramen as the ligament is completely ossified.

Trapezoid ligament

The trapezoid ligament, the anterior and lateral fasciculus, is broad, thin, and quadrilateral: it is placed obliquely between the coracoid process and the clavicle.

It is attached, below, to the upper surface of the coracoid process; above, to the oblique ridge on the under surface of the clavicle.

Its anterior border is free; its posterior border is joined with the conoid ligament, the two forming, by their junction, an angle projecting backward.

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