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Forelimb - Anatomy & Physiology (view source)
Revision as of 19:33, 27 October 2022
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==Common structures of the Proximal Forelimb and Shoulder==
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==Common Structures of the Proximal Forelimb and Shoulder==
===Scapula===
===Scapula===
The Scapula forms the basis of the shoulder region, providing points of attachment of extrinsic and intrinsic muscles. It is held in place by a synsarcosis of muscles and does not form a conventional articulation with the trunk. In ungulates, the dorsal border is extended by a scapular cartilage, which enlarges the area for muscle attachment. This ossifies with age. The bone is roughly triangular, with a prominent '''spine''' that can be palpated through the skin.
The Scapula forms the basis of the shoulder region, providing points of attachment of extrinsic and intrinsic muscles. It is held in place by a synsarcosis of muscles and does not form a conventional articulation with the trunk. In ungulates, the dorsal border is extended by a scapular cartilage, which enlarges the area for muscle attachment. This ossifies with age. The bone is roughly triangular, with a prominent '''spine''' that can be palpated through the skin.
:The spine:
:The spine:
::defines '''Infraspinous''' and '''Supraspinous''' '''Fossae''', inhabited by muscles accordingly
::defines '''infraspinous''' and '''supraspinous''' '''fossae''', inhabited by the infraspinatus and supraspinatus muscles respectively
::serves as a point of attachment for the '''trapezius''' muscle
::serves as a point of attachment for the '''trapezius''' muscle
::culminates in the '''acromion''' in all but the horse and pig
::culminates in the '''acromion''' in all but the horse and pig.
::the cat also possesses a suprahamate process which lies proximal to the acromion and projects caudally.
Just cranial to the glenoid cavity can be seen a bony prominence called the supraglenoid tubercle which is the origin of the biceps bracii muscle
Medial muscle attachment consist mostly of the '''subscapularis''', with the '''serratus ventralis''' attaching dorsally. The Scapula articulates with the humerus at the '''glenoid cavity'''.
Medial muscle attachment consist mostly of the '''subscapularis''', with the '''serratus ventralis''' attaching dorsally. The Scapula articulates with the humerus at the '''glenoid cavity'''.
===Humerus===
===Humerus===
The Humerus is the long bone of the forearm, articulating with the scapula to form the shoulder and the radius and ulna to form the elbow. In situ, it lies obliquely along the ventral thorax and is more horizontal in larger species.
The Humerus is the long bone of the arm, articulating with the scapula to form the shoulder and the radius and ulna to form the elbow. In situ, it lies obliquely along the ventral thorax and is more horizontal in larger species.
The head of the humerus comprises '''greater''' and '''lesser tubercles''', separated by an '''intertubercular groove''' through which runs the tendon of the '''biceps brachii'''. The shaft of the humerus takes on a characteristically twisted shape via a groove carrying the '''brachialis''' and '''radial nerve'''. Laterally, the '''deltoid tuberosity''' is palpable through the skin and connects to the head of the humerus via a ridge and merges distally with the '''crest of the humerus'''. Distally, the humerus culminates in a '''condyle''' which articulates to form the elbow.
The head of the humerus comprises '''greater''' and '''lesser tubercles''', separated by an '''intertubercular groove''' through which runs the tendon of the '''biceps brachii'''. The shaft of the humerus takes on a characteristically twisted shape via a groove carrying the '''brachialis''' and '''radial nerve'''. Laterally, the '''deltoid tuberosity''' is palpable through the skin and connects to the head of the humerus via a ridge and merges distally with the '''crest of the humerus'''. Distally, the humerus culminates in a '''condyle''' which articulates to form the elbow.
:In large animals, it meets the radius via a '''trochlea'''
:In large animals, it meets the radius via a '''trochlea'''
:In dogs and cats, it articulates with the radius medially via a trochlea and the ulna laterally via a '''capitulum'''
:In dogs and cats, it articulates with the ulna medially via a trochlea and the radius laterally via a '''capitulum'''
:Caudally, all species show an '''olecranon fossa''' which articulates with the '''olecranon''' of the ulna
:Caudally, all species show an '''olecranon fossa''' which articulates with the '''olecranon''' of the ulna
At the distal end of the humerus a small hole may be seen connecting the olecranon fossa caudally with the radial fossa cranially. This is the supratrochlear foramen. No structures pass through it.
Medial and lateral epicondyles provide attachment for flexors and extensors of the carpus and digits.
Medial and lateral epicondyles provide attachment for flexors and extensors of the carpus and digits.
==Joints of the Proximal Forelimb==
==Joints of the Proximal Forelimb==
It is important to distinguish the shoulder/scapulohumeral joint from the entirely muscular connection (synsarcosis) between the forelimb and the trunk. This latter connection is sometimes called the '''girdle muscles''', although this is a problematic term, because many of its constituent muscles do not attach to a limb girdle muscle. At Cambridge University, it has for some time been given the name '''omothoracic junction''', but this term has not entered common usage.
It is important to distinguish the shoulder/scapulohumeral joint from the entirely muscular connection (synsarcosis) between the forelimb and the trunk. This latter connection is sometimes called the '''girdle muscles''', although this is a problematic term, because many of its constituent muscles do not attach to a limb girdle muscle. At Cambridge University, it has for some time been given the name '''omothoracic junction''', but this term has not entered common usage.
There are no true ligaments in the shoulder joint. The tendons of insertion of the supraspinatous and infraspinatous muscles cross the shoulder joint and insert laterally on the greater tubercle of the humerus. The tendon of the subscapularis inserts medially on the humerus. These act as 'ligaments' preventing dislocation of the shoulder.
===Elbow Joint===
===Elbow Joint===
===Ulna===
===Ulna===
The Ulna's greatest contribution to functional anatomy is in the formation of the '''olecranon''', or the point of the elbow, which gives rise to the attachment of the '''triceps''' muscle. The olecranon articulates with the humerus via its anconeal process. Distally (where unfused), the '''lateral styloid process''' articulates with the '''ulnar carpal bone'''.
The Ulna's greatest contribution to functional anatomy is in the formation of the '''olecranon''', or the point of the elbow, which gives rise to the attachment of the '''triceps''' muscle. The olecranon articulates with the humerus via its anconeal process. The olecranon develops as an apophysis, i.e.. from a separate site of ossification. The trochlear notch on the cranial aspect of the ulna articulates with the large trochlea of the humerus which forms the main elbow joint capable of flexion and extension. Just distal to the trochlear notch, a large medial '''coronoid process''' and a smaller lateral coronoid process can be seen. Distally (where unfused), the '''lateral styloid process''' articulates with the '''ulnar carpal bone'''.
===Carpal bones===
===Carpal bones===
===Metacarpal Joint===
===Metacarpal Joint===
The metacarpal joint is defined by the presence of palmar [[Bones - Anatomy & Physiology#Types of Bone|'''sesamoids''']], which allow the flexor tendons to pass over the sharp change in angle presented by the joint. They are paired on each digit, with the exception of the first digit where it exists.
The metacarpal joint is defined by the presence of palmar [[Bones - Anatomy & Physiology#Types of Bone|'''sesamoids''']], which allow the flexor tendons to pass over the sharp change in angle presented by the joint. They are paired on each digit, with the exception of the first digit where only one exists. A single '''dorsal sesamoid bone''' can also be seen in dogs in digit 2 - 5 inclusive over the same joint between the metacarpal bone and the proximal phalanx. This is not found in ungulates or in the the first digit. However another sesamoid bone exists in the tendon of the abductor pollicis longus muscle of the first digit.
==Muscles of the Forelimb==
==Muscles of the Forelimb==
'''''Pectoral mm.''''':
'''''Pectoral mm.''''':
:Innervated by: brachial plexus
:Innervated by: brachial plexus
::superficial pectoral m. - ventral branches of cervical spinal nerves 7 and 8 (Evans and de Lahunta's Guide to the Dissection of the Dog, 8th ed.)
::deep pectoral m. - caudal pectoral nerves, cervical spinal nerve 8, and thoracic nerve 1 (Evans and de Lahunta's Guide to the Dissection of the Dog, 8th ed.)
:Two superficial parts, cranial and caudal
:Two superficial parts, cranial and caudal
Medial:
Medial:
'''Subscapularis''':
:Innervated by: Subscapular n. from the brachial plexus
:Origin: Deep surface of the scapula
:Origin: Deep surface of the scapula
:Insertion: medial tubercle of the humerus
:Insertion: medial tubercle of the humerus
====Muscles of the Elbow====
====Muscles of the Elbow====
''Extensors'': Radial n. from the brachial plexus
''Extensors'':
:Innervated by: Radial n. from the brachial plexus
''Flexors'': Musculocutaneous n. from the brachial plexus
:'''Triceps brachii''': Three heads, four in the dog
::Long head: caudal margin of the scapula
::Lateral, medial, and accessory heads: shaft of the humerus
::Insertion: olecranon, proteced by tricipital bursa against the bone and subcutaneous bursa against the skin
:'''Tensor fasciae antebrachii'''
::Overlies triceps extending from scapula to olecranon
:'''Anconeus'''
::Origin: distal humerus
::Insertion: lateral olecranon
''Flexors'':
:Innervated by: Musculocutaneous n. from the brachial plexus
:'''Biceps brachii'''
::Origin: supraglenoid tubercle of the scapula
::Insertion: medial tuberosity of proximal radius and adjacent ulna
::Runs through the intertubercular groove of the humerus
:'''Brachialis'''
::Origin: proximocaudal humerus
::Insertion: spirals to insert next to biceps
====Muscles of Supination and Pronation ====
====Muscles of Supination and Pronation ====
''Supinators'': Radial n. from the brachial plexus
''Supinators'':
:Innervated by: Radial n. from the brachial plexus
:'''Brachioradialis'''
::Origin: lateral epicondyle of the humerus
::Insertion: distal medial forearm within superficial fascia
::Prominent in the cat but nearly absent in the dog
:'''Supinator'''
::Deep to extensor muscles, passing from lateral humeral epicondyles to upper medial radius
''Pronators'': Median n. from the brachial plexus
''Pronators'':
:Innervated by: Median n. from the brachial plexus
:'''Pronator teres''': only functional in cat and dog
::Origin: medial epicondyle of the humerus
::Insertion: supinator
:'''Pronator quadratus''': only found in carnivores
::Origin: shaft of the ulna
::Insertion: shaft of the radius
====Muscles of the Carpal and Digital Joints====
====Muscles of the Carpal and Digital Joints====
''Extensors'': Radial n. from the brachial plexus
''Extensors'':
:Innervated by: Radial n. from the brachial plexus
:Craniolateral position on the forearm
:Almost all originate from the lateral epicondyle of the humerus
:'''Extensor carpi radialis''': most medial, inserts on 2nd/3rd metacarpal bone
:'''Ulnaris lateralis''': most lateral, inserts on accessory carpal bone
:'''Extensor carpi obliquus''': aka '''abductor pollicis longus'''
::Origin: cranial radius
::Insertion: most medial metacarpal bone
:Last two may also serve in medial deviation of the paw
:'''Common Digital Extensor'''
::Insertion: extensor process of the distal phalanx of each digit
::Sends a medial branch to dew claw and medial digits in all but horse and cat
:'''Lateral Digital Extensor'''
::Insertion: dorsal proximal phalanx
''Flexors'':
:Innervated by: Median or Ulnar n. of the brachial plexus
:Caudal position on the forearm
:Originate from the caudal medial epicondyle of the humerus
:'''Flexor carpi radialis''': most medial, inserts on upper 2nd/3rd metacarpal bone
:'''Flexor carpi ulnaris''': most lateral, inserts on the accessory carpal bone
:'''Superficial Digital Flexor'''
::Branches according to the number of digis and inserts in proximal interphalangeal joint
:'''Deep Digital Flexor'''
::Passes through carpal canal before branching and continues to palmar distal phalanges
''Interosseus muscles''
''Interosseus muscles''
:Support metacarpophalnageal joints
:Arise from palmar proximal metacarpal bones and insert on sesamoid bones within the joints, continued by ligaments to phalanges
==Vasculature of the Forelimb==
==Vasculature of the Forelimb==
==Species Specifics==
==Species Specifics==
===[[Canine Forelimb - Anatomy & Physiology|Canine Forelimb]]===
===[[Canine Forelimb - Anatomy & Physiology|Canine Forelimb]]===
===[[Bovine Forelimb - Anatomy & Physiology|Bovine Forelimb]]===
===[[Bovine Forelimb - Anatomy & Physiology|Bovine Forelimb]]===
{{Template:Learning
|OVAM = [http://www.onlineveterinaryanatomy.net/content/muscle-flashcards-forelimb-extrinsics-quicktime Muscle flashcards - extrinsic musculature of the canine forelimb]<br>[http://www.onlineveterinaryanatomy.net/content/muscle-flashcards-shoulder-quicktime Muscle flashcards - muscles of the canine shoulder]<br>[http://www.onlineveterinaryanatomy.net/content/muscle-flashcards-elbow-quicktime Muscle flashcards - muscles of the canine elbow]<br>[http://www.onlineveterinaryanatomy.net/content/muscle-flashcards-antebrachium-quicktime Muscle flashcards - muscles of canine antebrachium]
}}
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[[Category:Musculoskeletal System - Anatomy & Physiology]]
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