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Dogs are '''digitigrade''' animals; this means that the weightbearing surface of their limbs is their digit. The canine phalanges are thus very important. They are virtually identical in their structure in the hindlimb and forelimb. The main differences are in the forelimb we have metacarpals and the metacarpophalangeal joint, the hindlimb equivalents are the metatarsals and the metatarsophalangeal joint. Also in anatomical planes we use the term palmar for forelimb and plantar for hindlimb. These terms are all interchangable in the below article depending on whether you want to talk about the fore or hindlimb.  

Dogs are '''digitigrade''' animals; this means that the weightbearing surface of their limbs is their digit. The canine phalanges are thus very important. They are virtually identical in their structure in the hindlimb and forelimb. The main differences are in the forelimb we have metacarpals and the metacarpophalangeal joint, the hindlimb equivalents are the metatarsals and the metatarsophalangeal joint. Also in anatomical planes we use the term palmar for forelimb and plantar for hindlimb. These terms are all interchangable in the below article depending on whether you want to talk about the fore or hindlimb.  

==Bones==

==Bones==

====Metacarpals and Metatarsals====

====Metacarpals and Metatarsals====

* The distal end is it's head, which is transversely cylindrical and articulates with the proximal phalanx.  

* The distal end is it's head, which is transversely cylindrical and articulates with the proximal phalanx.  

* Metacarpals II - V possess a sagittal ridge on their palmar aspects.  

* Metacarpals II - V possess a sagittal ridge on their palmar aspects.  

====Phalanges====

====Phalanges====

* Proximal phalanx - of the main digits (II - V) they have a concave articular surface proximally. The palmar border has a groove to accomodate the articular surface of the metacarpus when the joint is fixed. The distal head has two convex areas seperated by a groove.

* Proximal phalanx - of the main digits (II - V) they have a concave articular surface proximally. The palmar border has a groove to accomodate the articular surface of the metacarpus when the joint is fixed. The distal head has two convex areas seperated by a groove.

* Middle phalanx - roughly two-thirds the length of the proximal, its base has a sagittal ridge on the articular surface, which articulates with the groove of the proximal phalanx. The head resembles that of the proximal.

* Middle phalanx - roughly two-thirds the length of the proximal, its base has a sagittal ridge on the articular surface, which articulates with the groove of the proximal phalanx. The head resembles that of the proximal.

==Joints==

==Joints==

====Metacarpophalangeal Joint====

====Metacarpophalangeal Joint====

* Movement - flexion and extension.  

* Movement - flexion and extension.  

====Proximal Interphalangeal Joint====

====Proximal Interphalangeal Joint====

* Movement - flexion and extension.

* Movement - flexion and extension.

* The joint capsule attaches near the articular surfaces of the proximal and middle phalanges. It extends slightly in a pouch dorsally and more extensively on the palmar aspect. The dorsal capsule is reinforced by a fibrocartilaginous nodule; the extensor tendon attaches to the capsule here.

* The joint capsule attaches near the articular surfaces of the proximal and middle phalanges. It extends slightly in a pouch dorsally and more extensively on the palmar aspect. The dorsal capsule is reinforced by a fibrocartilaginous nodule; the extensor tendon attaches to the capsule here.

* '''Collateral ligaments''' - connect the distal end of the proximal phalanx to the proximal end of the middle phalanx. They lie in a vertical direction rather than along the bone axis.

* '''Collateral ligaments''' - connect the distal end of the proximal phalanx to the proximal end of the middle phalanx. They lie in a vertical direction rather than along the bone axis.

====Distal Interphalangeal Joint====

====Distal Interphalangeal Joint====

* Movement - extension, slight flexion.  

* Movement - extension, slight flexion.  

* The joint capsule attaches to the articular periphery of the bones and has a small fibrocartilagenous bead in the palmar aspect.

* The joint capsule attaches to the articular periphery of the bones and has a small fibrocartilagenous bead in the palmar aspect.

* '''Collateral ligaments''' - connect the distal part of the middle phalanx to the sides of the ungual crest of the distal phalanx.  

* '''Collateral ligaments''' - connect the distal part of the middle phalanx to the sides of the ungual crest of the distal phalanx.  

* '''Dorsal ligament''' - connects the proximal dorsal border of the extensor process of the distal phalanx. These are paired in dogs and function is to keep the claw raised until contraction of the deep digital flexor acts to overcome their tension.

* '''Dorsal ligament''' - connects the proximal dorsal border of the extensor process of the distal phalanx. These are paired in dogs and function is to keep the claw raised until contraction of the deep digital flexor acts to overcome their tension.

==Musculature==

==Musculature==

'''Interosseous'''

'''Interosseous'''

* Function - support of the metacarpophalangeal joints.

* Function - support of the metacarpophalangeal joints.

====Forelimb====

====Forelimb====

'''Superficial digital flexor'''

'''Superficial digital flexor'''

* Function - flexion of the digits

* Function - flexion of the digits

* Origin - medial epicondyle of the humerus

* Origin - medial epicondyle of the humerus

* Insertion - palmar aspect of the middle phalanges

* Insertion - palmar aspect of the middle phalanges

'''Deep digital flexor'''

'''Deep digital flexor'''

* Origin - medial epicondyle of the humerus, proximal radius and ulna

* Origin - medial epicondyle of the humerus, proximal radius and ulna

* Insertion - palmar aspect of distal phalanges

* Insertion - palmar aspect of distal phalanges

'''Common digital extensor'''

'''Common digital extensor'''

* Origin - lateral epicondyle of the humerus

* Origin - lateral epicondyle of the humerus

* Insertion - extensor process, distal phalanx

* Insertion - extensor process, distal phalanx

'''Lateral digital extensor'''

'''Lateral digital extensor'''

* Origin - lateral epicondyle of the humerus

* Origin - lateral epicondyle of the humerus

* Insertion - proximal phalanx

* Insertion - proximal phalanx

====Hindlimb====

====Hindlimb====

'''Long Digital Extensor'''

'''Long Digital Extensor'''

* Insertion - flexor aspect of the tarsus and branches which continue onto the extensor process of each of the distal phalanges.

* Insertion - flexor aspect of the tarsus and branches which continue onto the extensor process of each of the distal phalanges.

* It divides into four branches at the level of the tarsus and are bound by the fibrous transverse bands of the proximal and distal retinaculum and are enclosed by a common synovial sheath.

* It divides into four branches at the level of the tarsus and are bound by the fibrous transverse bands of the proximal and distal retinaculum and are enclosed by a common synovial sheath.

'''Lateral Digital Extensor'''

'''Lateral Digital Extensor'''

* Origin - proximal fibula and lateral collateral ligament of the stifle.

* Origin - proximal fibula and lateral collateral ligament of the stifle.

* Insertion - It joins to the tendon of the long digital extensor to insert on the distal phalanx of the 5th digit.

* Insertion - It joins to the tendon of the long digital extensor to insert on the distal phalanx of the 5th digit.

'''Long Extensor of the first digit'''

'''Long Extensor of the first digit'''

* Origin - Proximal fibula

* Origin - Proximal fibula

* Insertion - the metatarsophalangeal joint of the 2nd and 1st digit.

* Insertion - the metatarsophalangeal joint of the 2nd and 1st digit.

'''Superficial Digital Flexor'''

'''Superficial Digital Flexor'''

* A '''synovial bursa''' lies between this cap and the calcaneal tuberosity.

* A '''synovial bursa''' lies between this cap and the calcaneal tuberosity.

* It then runs over the plantar aspect of the hock and splits twice at the level of the dorsal tarsal bones, thus forming it's four branches for insertion.

* It then runs over the plantar aspect of the hock and splits twice at the level of the dorsal tarsal bones, thus forming it's four branches for insertion.

'''Deep Digital Flexor'''

'''Deep Digital Flexor'''

==The Canine Paw==

==The Canine Paw==

Composed of four weight-bearing toes, each with a claw and footpad. In addition there is a metacarpal/metatarsal footpad.

Composed of four weight-bearing toes, each with a claw and footpad. In addition there is a metacarpal/metatarsal footpad.

* The claws grow at rapid rate and so if they aren't worn by active wear they must be trimmed. Care must be taken as the dermis is highly vascular and bleeding will occur if cut into. To ensure that only the epidermis is cut take great care.

* The claws grow at rapid rate and so if they aren't worn by active wear they must be trimmed. Care must be taken as the dermis is highly vascular and bleeding will occur if cut into. To ensure that only the epidermis is cut take great care.

[[Category:Musculoskeletal System]]

[[Category:Musculoskeletal System - Anatomy & Physiology]]