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Learning Objectives
- Identify the muscles of the pectoral girdle and upper limbs
- Identify the movement and function of the pectoral girdle and upper limbs
Muscles of the shoulder and upper limb can be divided into four groups: muscles that stabilize and position the pectoral girdle, muscles that move the arm, muscles that move the forearm, and muscles that move the wrists, hands, and fingers. The pectoral girdle, or shoulder girdle, consists of the lateral ends of the clavicle and scapula, along with the proximal end of the humerus, and the muscles covering these three bones to stabilize the shoulder joint. The girdle creates a base from which the head of the humerus, in its ball-and-socket joint with the glenoid fossa of the scapula, can move the arm in multiple directions.
Muscles That Position the Pectoral Girdle
Muscles that position the pectoral girdle are located either on the anterior thorax or on the posterior thorax (Figure 1 and Table 1).
The anterior muscles include the subclavius, pectoralis minor, and serratus anterior. The posterior muscles include the trapezius, rhomboid major, and rhomboid minor. When the rhomboids are contracted, your scapula moves medially, which can pull the shoulder and upper limb posteriorly.
| Table 1. Muscles that Position the Pectoral Girdle | ||||||
|---|---|---|---|---|---|---|
| Position in the Thorax | Movement | Target | Target motion direction | Prime mover | Origin | Insertion |
| Anterior thorax | Stabilizes clavicle during movement by depressing it | Clavicle | Depression | Subclavius | First rib | Inferior surface of clavicle |
| Anterior thorax | Rotates shoulder anteriorly (throwing motion); assists with inhalation | Scapula; ribs | Scapula: depresses; ribs: elevates | Pectoralis minor | Anterior surfaces of certain ribs (2–4 or 3–5) | Coracoid process of scapula |
| Anterior thorax | Moves arm from side of body to front of body; assists with inhalation | Scapula; ribs | Scapula: protracts; ribs: elevates | Serratus anterior | Muscle slips from certain ribs (1–8 or 1–9) | Anterior surface of vertebral border of scapula |
| Posterior thorax | Elevates shoulders (shrugging); pulls shoulder blades together; tilts head backwards | Scapula; cervical spine | Scapula: rotates inferiorly, retracts, elevates, and depresses; spine: extends | Trapezius | Skull; vertebral column | Acromion and spine of scapula; clavicle |
| Posterior thorax | Stabilizes scapula during pectoral girdle movement | Scapula | Retracts; rotates inferiorly | Rhomboid major | Thoracic vertebrae (T2–T5) | Medial border of scapula |
| Posterior thorax | Stabilizes scapula during pectoral girdle movement | Scapula | Retracts; rotates inferiorly | Rhomboid minor | Cervical and thoracic vertebrae (C7 and T1) | Medial border of scapula |
Muscles That Move the Humerus
Similar to the muscles that position the pectoral girdle, muscles that cross the shoulder joint and move the humerus bone of the arm include both axial and scapular muscles (Figure 2, Figure 3, and Table 2).
The two axial muscles are the pectoralis major and the latissimus dorsi. The pectoralis major is thick and fan-shaped, covering much of the superior portion of the anterior thorax. The broad, triangular latissimus dorsi is located on the inferior part of the back, where it inserts into a thick connective tissue shealth called an aponeurosis.
| Table 2. Muscles That Move the Humerus | |||||
|---|---|---|---|---|---|
| Movement | Target | Target motion direction | Prime mover | Origin | Insertion |
| Axial muscles | |||||
| Brings elbows together; moves elbow up (as during an uppercut punch) | Humerus | Flexion; adduction; medial rotation | Pectoralis major | Clavicle; sternum; cartilage of ribs (1–6 or 1–7); aponeurosis of external oblique muscle | Greater tubercle of humerus |
| Moves elbow back (as in elbowing someone standing behind you); spreads elbows apart | Humerus; scapula | Humerus: extension, adduction, and medial rotation; scapula: depression | Latissimus dorsi | Thoracic vertebrae (T7–T12); lumbar vertebrae; lower ribs (9–12); iliac crest | Intertubercular sulcus of humerus |
| Scapular muscles | |||||
| Lifts arms at the shoulder | Humerus | Abduction; flexion; extension; medial and lateral rotation | Deltoid | Trapezius; clavicle; acromion; spine of scapula | Nasal bone |
| Assists the pectoralis major in bringing the elbows together and stabilizes the shoulder joint during movement of the pectoral girdle | Humerus | Medial rotation | Subscapularis | Subscapular fossa of the scapula | Lesser tubercle of humerus |
| Rotates the elbow outwards, as during a tennis swing | Humerus | Abduction | Supraspinatus | Supraspinous fossa of the scapula | Greater tubercle of humerus |
| Rotates the elbow outwards, as during a tennis swing | Humerus | Extension; adduction | Infraspinatus | Infraspinous fossa of the scapula | Greater tubercle of humerus |
| Assists the infraspinatus in rotating the elbow outwards | Humerus | Extension; adduction | Teres major | Posterior surface of the scapula | Intertubercular sulcus of humerus |
| Assists the infraspinatus in rotating the elbow outwards | Humerus | Extension; adduction | Teres minor | Lateral border of the dorsal scapular surface | Greater tubercle of humerus |
| Moves the elbow up and across the body, as when putting a hand on the chest | Humerus | Flexion; adduction | Coracobra chialis | Coracoid process of the scapula | Medial surface of humerus shaft |
The rest of the shoulder muscles originate on the scapula. The anatomical and ligamental structure of the shoulder joint and the arrangements of the muscles covering it, allows the arm to carry out different types of movements. The deltoid, the thick muscle that creates the rounded lines of the shoulder is the major abductor of the arm, but it also facilitates flexing and medial rotation, as well as extension and lateral rotation. The subscapularis originates on the anterior scapula and medially rotates the arm. Named for their locations, the supraspinatus (superior to the spine of the scapula) and the infraspinatus (inferior to the spine of the scapula) abduct the arm, and laterally rotate the arm, respectively. The thick and flat teres major is inferior to the teres minor and extends the arm, and assists in adduction and medial rotation of it. The long teres minor laterally rotates and extends the arm. Finally, the coracobrachialis flexes and adducts the arm.
The tendons of the deep subscapularis, supraspinatus, infraspinatus, and teres minor connect the scapula to the humerus, forming the rotator cuff (musculotendinous cuff), the circle of tendons around the shoulder joint. When baseball pitchers undergo shoulder surgery it is usually on the rotator cuff, which becomes pinched and inflamed, and may tear away from the bone due to the repetitive motion of bring the arm overhead to throw a fast pitch.
Muscles That Move the Forearm
The forearm, made of the radius and ulna bones, has four main types of action at the hinge of the elbow joint: flexion, extension, pronation, and supination. The forearm flexors include the biceps brachii, brachialis, and brachioradialis. The extensors are the triceps brachii and anconeus. The pronators are the pronator teres and the pronator quadratus, and the supinator is the only one that turns the forearm anteriorly. When the forearm faces anteriorly, it is supinated. When the forearm faces posteriorly, it is pronated.
The biceps brachii, brachialis, and brachioradialis flex the forearm. The two-headed biceps brachii crosses the shoulder and elbow joints to flex the forearm, also taking part in supinating the forearm at the radioulnar joints and flexing the arm at the shoulder joint. Deep to the biceps brachii, the brachialis provides additional power in flexing the forearm. Finally, the brachioradialis can flex the forearm quickly or help lift a load slowly. These muscles and their associated blood vessels and nerves form the anterior compartment of the arm (anterior flexor compartment of the arm) (Figure 4 and Table 3).
| Table 3. Muscles That Move the Forearm | |||||
|---|---|---|---|---|---|
| Movement | Target | Target motion direction | Prime mover | Origin | Insertion |
| Anterior muscles (flexion) | |||||
| Performs a bicep curl; also allows palm of hand to point toward body while flexing | Forearm | Flexion; supination | Biceps brachii | Coracoid process; tubercle above glenoid cavity | Radial tuberosity |
| Forearm | Flexion | Brachialis | Front of distal humerus | Coronoid process of ulna | |
| Assists and stabilizes elbow during bicep-curl motion | Forearm | Flexion | Brachioradialis | Lateral supracondylar ridge at distal end of humerus | Base of styloid process of radius |
| Posterior muscles (extension) | |||||
| Extends forearm, as during a punch | Forearm | Extension | Triceps brachii | Infraglenoid tubercle of scapula; posterior shaft of humerus; posterior humeral shaft distal to radial groove | Olecranon process of ulna |
| Assists in extending forearm; also allows forearm to extend away from body | Forearm | Extension; abduction | Anconeus | Lateral epicondyle of humerus | Lateral aspect of olecranon process of ulna |
| Anterior muscles (pronation) | |||||
| Turns hand palm-down | Forearm | Pronation | Pronator teres | Medial epicondyle of humerus; coronoid process of ulna | Lateral radius |
| Assists in turning hand palm-down | Forearm | Pronation | Pronator quadratus | Distal portion of anterior ulnar shaft | Distal surface of anterior radius |
| Posterior muscles (supination) | |||||
| Tuns hand palm-up | Forearm | Supination | Supinator | Lateral epicondyle of humerus; proximal ulna | Proximal end of radius |
Muscles That Move the Wrist, Hand, and Fingers
Wrist, hand, and finger movements are facilitated by two groups of muscles. The forearm is the origin of the extrinsic muscles of the hand. The palm is the origin of the intrinsic muscles of the hand.
Muscles of the Arm That Move the Wrists, Hands, and Fingers
The muscles in the anterior compartment of the forearm (anterior flexor compartment of the forearm) originate on the humerus and insert onto different parts of the hand. These make up the bulk of the forearm. From lateral to medial, the superficial anterior compartment of the forearm includes the flexor carpi radialis, palmaris longus, flexor carpi ulnaris, and flexor digitorum superficialis. The flexor digitorum superficialis flexes the hand as well as the digits at the knuckles, which allows for rapid finger movements, as in typing or playing a musical instrument (see Table 4). However, poor ergonomics can irritate the tendons of these muscles as they slide back and forth with the carpal tunnel of the anterior wrist and pinch the median nerve, which also travels through the tunnel, causing Carpal Tunnel Syndrome. The deep anterior compartment produces flexion and bends fingers to make a fist. These are the flexor pollicis longus and the flexor digitorum profundus.
The muscles in the superficial posterior compartment of the forearm (superficial posterior extensor compartment of the forearm) originate on the humerus. These are the extensor radialis longus, extensor carpi radialis brevis,extensor digitorum, extensor digiti minimi, and the extensor carpi ulnaris.
The muscles of the deep posterior compartment of the forearm (deep posterior extensor compartment of the forearm) originate on the radius and ulna. These include the abductor pollicis longus, extensor pollicis brevis,extensor pollicis longus, and extensor indicis (see Table 4).
| Table 4. Muscles That Move the Wrist, Hands, and Forearm | |||||
|---|---|---|---|---|---|
| Movement | Target | Target motion direction | Prime mover | Origin | Insertion |
| Superficial anterior compartment of forearm | |||||
| Bends the wrist toward the body; it also tilts the hand to the side away from the body | Wrist; hand | Flexion; abduction | Flexor carpi radialis | Medial epicondyle of the humerus | Base of second and third metacarpals |
| Assists in bending the hand up toward the shoulder | Wrist | Flexion | Palmaris longus | Medial epicondyle of the humerus | Palmar aponeurosis; skin and fascia of palm |
| Assists in bending the hand up toward the shoulder; it also tilts the hand to the side away from the body and stabilizes the wrist | Wrist; hand | Flexion; abduction | Flexor carpi ulnaris | Medial epicondyle of the humerus, the olecranon process, and the posterior surface of the ulna | Pisiform, hamate bones, and base of fifth metacarpal |
| Bends the fingers to make a fist | Wrist; fingers 2–5 | Flexion | Flexor digitorum superficialis | Medial epicondyle of the humerus, the coronoid process of the ulna, and the shaft of the radius | Middle phalanges of fingers 2–5 |
| Deep anterior compartment of forearm | |||||
| Bends the tip of the thumb | Thumb | Flexion | Flexor pollicis longus | Anterior surface of the radius and the interosseous membrane | Distal phalanx of thumb |
| Bends the fingers to make a fist; it also bends the wrist toward the body | Wrist; fingers | Flexion | Flexor digitorum profundus | Coronoid process, the anteromedial surface of the ulna, and the interosseous membrane | Distal phalanges of fingers 2–5 |
| Superficial posterior compartment of forearm | |||||
| Straightens the wrist away from the body; it also tilts the hand to the side away from the body | Wrist | Extension; abduction | Extensor radialis longus | Lateral supracondylar ridge of the humerus | Base of second metacarpal |
| Assists the extensor radialis longus in extending and abducting the wrist; it also stabilizes the hand during finger flexion | Wrist | Extension; abduction | Extensor carpi radialis brevis | Lateral epicondyle of the humerus | Base of third metacarpal |
| Opens the fingers and moves them sideways away from the body | Wrist; fingers | Extension; abduction | Extensor digitorum | Lateral epicondyle of the humerus | Extensor expansions; distal phalanges of fingers |
| Extends the little finger | Little finger | Extension | Extensor digiti minimi | Lateral epicondyle of the humerus | Extensor expansion; distal phalanx of finger 5 |
| Straightens the wrist away from the body; it also tilts the hand to the side toward the body | Wrist | Extension; abduction | Extensor carpi ulnaris | Lateral epicondyle of the humerus and the posterior of the ulna | Base of fifth metacarpal |
| Deep posterior compartment of forearm | |||||
| Moves the thumb sideways toward the body; it also extends the thumb and moves the hand sideways toward the body | Wrist; thumb | Thumb: abduction, extension; wrist: abduction | Abductor pollicis longus | Posterior surface of the radius and ulna and in the interosseous membrane | Base of first metacarpal; trapezium |
| Extends the thumb | Thumb | Extension | Extensor pollicis brevis | Dorsal shaft of the radius and ulna and in the interosseous membrane | Base of proximal phalanx of thumb |
| Extends the thumb | Thumb | Extension | Extensor pollicis longus | Dorsal shaft of the radius and ulna and in the interosseous membrane | Base of distal phalanx of thumb |
| Extends the index finger; it also straightens the wrist away from the body | Wrist; index finger | Extension | Extensor indicis | Posterior surface of the distal ulna and in the interosseous membrane | Tendon of extensor digitorum of finger |
The tendons of the forearm muscles attach to the wrist and extend into the hand. Fibrous bands called retinacula sheath the tendons at the wrist. The flexor retinaculum extends over the palmar surface of the hand while the extensor retinaculum extends over the dorsal surface of the hand.
Intrinsic Muscles of the Hand
The intrinsic muscles of the hand both originate and insert within it (Figure 5). These muscles allow your fingers to also make precise movements for actions, such as typing or writing. These muscles are divided into three groups. The thenar muscles are on the radial aspect of the palm. The hypothenar muscles are on the medial aspect of the palm, and the intermediate muscles are midpalmar.
The thenar muscles include the abductor pollicis brevis, opponens pollicis, flexor pollicis brevis, and the adductor pollicis. These muscles form the thenar eminence, the rounded contour of the base of the thumb, and all act on the thumb. The movements of the thumb play an integral role in most precise movements of the hand.
The hypothenar muscles include the abductor digiti minimi, flexor digiti minimi brevis, and the opponens digiti minimi. These muscles form the hypothenar eminence, the rounded contour of the little finger, and as such, they all act on the little finger. Finally, the intermediate muscles act on all the fingers and include the lumbrical, the palmar interossei, and the dorsal interossei.
| Table 5. Muscles That Move the Wrist, Hands, and Forearm | ||||||
|---|---|---|---|---|---|---|
| Muscle | Movement | Target | Target motion direction | Prime mover | Origin | Insertion |
| Thenar muscles | Moves thumb toward body | Thumb | Abduction | Abductor pollicis brevis | Flexor retinaculum; nearby carpals | Lateral base of proximal phalanx of thumb |
| Thenar muscles | Moves thumb across palm toward body | Thumb | Opposition | Opponens pollicis | Flexor retinaculum; trapezium | Anterior of first metacarpal |
| Thenar muscles | Flexes thumb | Thumb | Flexion | Flexor pollicis brevis | Felxor retinaculum; trapezium | Lateral base of proximal phalanx of thumb |
| Thenar muscles | Moves thumb away from body | Thumb | Adduction | Adductor pollicis | Capitate bone; bases of metacarpals 2–4; front of metacarpal | Medial base of proximal phalanx of thumb |
| Hypothenar muscles | Moves little finger toward body | Little finger | Abduction | Abductor digiti minimi | Pisiform bone | Medial side of proximal phalanx of little finger |
| Hypothenar muscles | Flexes little finger | Little finger | Flexion | Flexor digiti minimi brevis | Hamate bone; flexor retinaculum | Medial side of proximal phalanx of little finger |
| Hypothenar muscles | Moves little finger across palm to touch thumb | Little finger | Opposition | Opponens digiti minimi | Hamate bone; flexor retinaculum | Medial side of proximal phalanx of little finger |
| Intermediate muscles | Flexes each finger at metacarpo-phalangeal joints; extends each finger at interphalangeal joints | Fingers | Flexion | Lumbricals | Palm (lateral sides of tendons in flexor digitorum profundus) | Fingers 2–5 (lateral edges of extensional expansions on first phalanges) |
| Intermediate muscles | Adducts and flexes each finger at meacarpo-phalangeal joints; extends each finger at interphalangeal joints | Fingers | Adduction; flexion; extension | Palmar interossei | Side of each metacarpal that faces metacarpal 3 (absent from metacarpal 3) | Extensor expansion on first phalanx of each finger (except finger 3) on side facing finger 3 |
| Intermediate muscles | Abducts and flexes the three middle fingers at metacarpo-phalangeal joints; extends the three middle fingers at interphalangeal joints | Fingers | Abduction; flexion; extension | Dorsal interossei | Sides of metacarpals | Both sides of finger 3; for each other finger, extensor expansion over first phalanx on side opposite finger 3 |
14.12: Muscles of the Pectoral Girdle and Upper Limbs - Biology
The appendicular skeleton is composed of the bones of the upper limbs (which function to grasp and manipulate objects) and the lower limbs (which permit locomotion). It also includes the pectoral girdle, or shoulder girdle, that attaches the upper limbs to the body, and the pelvic girdle that attaches the lower limbs to the body (Figure 1).
Figure 1. The appendicular skeleton is composed of the bones of the pectoral limbs (arm, forearm, hand), the pelvic limbs (thigh, leg, foot), the pectoral girdle, and the pelvic girdle. (credit: modification of work by Mariana Ruiz Villareal)
Anatomy
The pectoral girdle provides the main structural support for the shoulder joint. The pectoral girdle consists of two bones:
These bones of the pectoral girdle form several joints, including:
- Acromioclavicular (AC) joint: The acromioclavicular joint forms between the acromion of the scapula and the clavicle at the top of the shoulder.
- Sternoclavicular joint: The sternoclavicular joint forms between the sternum (breastbone) and clavicle at the front of the chest.
- Scapulothoracic joint: The scapulothoracic joint forms between the medial border (inner edge) of the scapula and the thoracic vertebrae of the upper spine.
The muscles that move the forearm and wrist (see Figure 4.29, 4.10) gen-erally have their origins in the humerus (except for biceps brachii and the triceps brachii) and cross the elbow and/or wrist joint. At the elbow, the muscles produce flexion and extension of the forearm. In addition, some muscles, by rotating the radius over the lower end of the ulna, pronate (palm faces pos-teriorly) and supinate (palm faces anteriorly) the forearm.
Flexion, extension, abduction, and adduction are movements that are brought about at the wrist. Notethat all the extensors arise on the lateral aspect of humerus.
Pectoral and Pelvic Girdle and Limbs - PowerPoint PPT Presentation
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presentations for free. Or use it to find and download high-quality how-to PowerPoint ppt presentations with illustrated or animated slides that will teach you how to do something new, also for free. Or use it to upload your own PowerPoint slides so you can share them with your teachers, class, students, bosses, employees, customers, potential investors or the world. Or use it to create really cool photo slideshows - with 2D and 3D transitions, animation, and your choice of music - that you can share with your Facebook friends or Google+ circles. That's all free as well!
What are the bones of the pectoral and pelvic girdles?
Shoulder girdle. The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula in those species with three bones in the shoulder, it consists of the clavicle, scapula, and coracoid.
Also Know, why are the bones of the pelvic girdle larger than the bones of the pectoral girdle? Why is it necessary for the bones of the pelvic girdle to be more massive than the bones of the pectoral girdle? : The pelvic girdle must withstand the load of bearing and moving the entire body whereas the pectoral girdle only supports the upper limbs.
Similarly, you may ask, what is the pelvic and pectoral girdle?
1. The pectoral girdle is situated in the pectoral region of the body and joins the upper limb to the body. The pelvic girdle is situated in the pelvic region of the body and joins the lower limb to the body. 2. It is composed of two bones namely clavicle or collar bone and scapula.
Origins of the tetrapod limbs
The invasion of land led to a complete change in emphasis in the propulsive elements of the muscular system. In fish the axial musculature is much more important as a mover of the body than is the appendicular musculature. The evolution of land vertebrates is characterized by an increasing emphasis on the limbs for propulsion and by a corresponding de-emphasis on the axial musculature. The limbs of tetrapods are generally similar in overall pattern. Primitively at least, most major groups have similar characteristic features: the fore and hind feet have five digits there is one bone in the proximal part of the limb (nearest to the body) and two in the distal part (away from the body) and there are a wrist or ankle joint, an elbow or knee joint, and a shoulder or hip joint. Although most muscles have several roles, the major actions of tetrapod limb muscles are similar: some primarily resist the downward force of the body at hip and shoulder, others press the supporting fore or hind feet down onto the ground at wrist or ankle or pull back on the supporting limbs (at all three joints) to create thrust, and others primarily pull the “swing” limbs forward into a new support position.
The limbs may originally have developed more as supportive struts. Structurally, the tetrapod limb can be derived from the pattern found in the paired fins of Sarcopterygii, a class of lobe-finned fishes. These were once a large radiation but have been largely replaced by the Actinopterygii, the class of ray-finned fishes. Today the lobe-finned fishes are represented by the coelacanth (Latimeria) and the lungfishes (Dipnoi). The lungfishes, denizens of shallow and seasonal waters, habitually use their fins as supports, but propulsion is largely achieved by undulations of the body, as is the case with other fish.
The anatomy and ontogeny of the head, neck, pectoral, and upper limb muscles of Lemur catta and Propithecus coquereli (primates): discussion on the parallelism between ontogeny and phylogeny and implications for evolutionary and developmental biology
Most anatomical studies of primates focus on skeletal tissues, but muscular anatomy can provide valuable information about phylogeny, functional specializations, and evolution. Herein, we present the first detailed description of the head, neck, pectoral, and upper limb muscles of the fetal lemuriforms Lemur catta (Lemuridae) and Propithecus coquereli (Indriidae). These two species belong to the suborder Strepsirrhini, which is often presumed to possess some plesiomorphic anatomical features within primates. We compare the muscular anatomy of the fetuses with that of infants and adults and discuss the evolutionary and developmental implications. The fetal anatomy reflects a phylogenetically more plesiomorphic condition in nine of the muscles we studied and a more derived condition in only two, supporting a parallel between ontogeny and phylogeny. The derived exceptions concern muscles with additional insertions in the fetus which are lost in adults of the same species, that is, flexor carpi radialis inserts on metacarpal III and levator claviculae inserts on the clavicle. Interestingly, these two muscles are involved in movements of the pectoral girdle and upper limb, which are mainly important for activities in later stages of life, such as locomotion and prey capture, rather than activities in fetal life. Accordingly, our findings suggest that some exceptions to the "ontogeny parallels phylogeny" rule are probably driven more by ontogenetic constraints than by adaptive plasticity.
Keywords: development head and neck morphology muscles primates strepsirrhines upper limb.
Reconstructing pectoral appendicular muscle anatomy in fossil fish and tetrapods over the fins-to-limbs transition
The question of how tetrapod limbs evolved from fins is one of the great puzzles of evolutionary biology. While palaeontologists, developmental biologists, and geneticists have made great strides in explaining the origin and early evolution of limb skeletal structures, that of the muscles remains largely unknown. The main reason is the lack of consensus about appendicular muscle homology between the closest living relatives of early tetrapods: lobe-finned fish and crown tetrapods. In the light of a recent study of these homologies, we re-examined osteological correlates of muscle attachment in the pectoral girdle, humerus, radius, and ulna of early tetrapods and their close relatives. Twenty-nine extinct and six extant sarcopterygians were included in a meta-analysis using information from the literature and from original specimens, when possible. We analysed these osteological correlates using parsimony-based character optimization in order to reconstruct muscle anatomy in ancestral lobe-finned fish, tetrapodomorph fish, stem tetrapods, and crown tetrapods. Our synthesis revealed that many tetrapod shoulder muscles probably were already present in tetrapodomorph fish, while most of the more-distal appendicular muscles either arose later from largely undifferentiated dorsal and ventral muscle masses or did not leave clear correlates of attachment in these taxa. Based on this review and meta-analysis, we postulate a stepwise sequence of specific appendicular muscle acquisitions, splits, and fusions that led from the ancestral sarcopterygian pectoral fin to the ancestral tetrapod forelimb. This sequence largely agrees with previous hypotheses based on palaeontological and comparative work, but it is much more comprehensive in terms of both muscles and taxa. Combined with existing information about the skeletal system, our new synthesis helps to illuminate the genetic, developmental, morphological, functional, and ecological changes that were key components of the fins-to-limbs transition.
Keywords: Acanthostega Eusthenopteron Pederpes Sarcopterygii Tetrapoda extant phylogenetic bracket stem tetrapods water-land transition.
© 2017 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.
Shoulder Girdle
Shoulder Girdle or pectoral girdle is the bony ring, incomplete behind, which serves for the attachment and support of the upper limbs. It is formed by the manubrium sterni, the clavicles, and the scapulae. In humans it consists of the clavicle and scapula in those species with three bones in the shoulder, it consists of the clavicle, scapula, and coracoid. Some mammalian species (such as the dog and the horse) have only the scapula.
Shoulder Girdle or pectoral girdle connects the upper limb to the axial skeleton on the left and right side of the body. There is an anatomical connection between the pectoral girdle and the axial skeleton that is, the sternoclavicular joints anteriorly.
There is a physiological joint – (scapulothoracic joint) or muscular connection between the shoulder girdle and the axial skeleton, which is formed by muscles including the trapezius, rhomboids and serratus anterior. This scapulothoracic joint is highly mobile and allows great movements of the shoulder girdle.
Structure and Functions of Shoulder Girdle
The shoulder joint is not held in place with bones, but rather an elaborate system of muscles, tendons and ligaments. Those most at risk for shoulder problems are athletes or workers with “overhead” movements—swimmers, throwers, painters and construction workers.
From its neutral position, the shoulder girdle can be rotated about an imaginary vertical axis at the medial end of the clavicle. Throughout this movement the scapula is rotated around the chest wall so that it moves 15 centimetres (5.9 in) laterally and the glenoid cavity is rotated 40–45° in the horizontal plane. The scapula can be elevated and depressed from the neutral position to a total range of 10 to 12 centimetres (3.9 to 4.7 in) at its most elevated position the scapula is always tilted so that the glenoid cavity is facing superiorly.
There are three joints in the shoulder girdle. One joint is where the head of the humerus articulates inside the glenoid cavity of the scapula, called the glenohumeral joint which includes the ligaments, tendons and muscles attached to these two bones. The acromioclavicular joint (A/C Joint) includes the ligaments, tendons, and bones where the acromion (on the shoulder blade) joins at the clavicle (collar bone). The third joint is the sternoclavicular joint which forms where the sternum (breastbone) joins the clavicle (collar bone).
Humerus (upper arm). The humerus is the ball part of the ball-and-socket joint. The head (ball) of the humerus articulates within the glenoid fossa. Below the humeral head is the anatomic neck which separates the head (ball) from the tuberosities.
