Muscles and Joints of the Forelimb Distal

Comprehensive vocabulary flashcards covering the distal forelimb joints, ligaments, muscles, fascial sheaths, and species-specific adaptations in the horse, ruminant, and carnivore.

Articulatio carpi (eq)

A composite joint (articulatio composita) that acts as a ginglymus (hinge) joint allowing flexion and extension. It connects the radius, carpus, and metacarpal bones. Its fibrous capsule covers the entire joint, while the synovial layer inserts on each row to form separate articular cavities.

Ligamentum collaterale carpi laterale

A collateral ligament arising from the processus styloideus lateralis radii and inserting onto the os carpi ulnare, os carpale IV+V, and metacarpal bones. It consists of a superficial long part and shorter, deeper parts forming proximal, middle, and distal limbs.

Ligamentum collaterale carpi mediale

A collateral ligament originating from the processus styloideus medialis radii and inserting onto the os carpi radiale, os carpale II, and metacarpal bones. It contains a superficial long band and shorter, deeper components forming proximal, middle, and distal limbs.

Articulatio antebrachiocarpea (articulatio radiocarpea, eq)

The joint formed between the trochlea of the radius and the proximal row of carpal bones. It features a very spacious joint capsule with a recessus lateropalmaris, allows $95^\circ$ of flexion, possesses a lig. radiocarpeum palmare, and lacks a lig. radiocarpeum dorsale (enabling extreme flexion).

Articulatio mediocarpea (eq)

The joint between the proximal and distal carpal rows allowing $45^\circ$ of flexion. Its joint cavity communicates with that of the articulatio carpometacarpea between os carpale III and os carpale IV+V, and it is reinforced palmarily by the lig. carpi radiatum.

Articulatio carpometacarpea (eq)

An amphiarthrosis joint between the distal carpal bones and the base of the metacarpal bones with tight joint capsules and minimal movement. It communicates directly with the articulatio mediocarpea and is stabilized by dorsal and palmar carpometacarpal ligaments.

Articulationes intercarpeae (eq)

Amphiarthrodial joints located between adjacent carpal bones within each row that permit minimal movement. They are united by short transversal ligg. intercarpea interossea, while dorsal intercarpal ligaments are absent in horses.

Articulatio ossis carpi accessorii (eq)

The joint formed between the accessory carpal bone and the ulnar carpal bone and radius. It is secured by four distinct ligaments: lig. accessorioulnare, lig. accessoriocarpoulnare, lig. accessorioquartale, and lig. accessoriometacarpeum.

Ligamentum carpi palmare profundum

A functional unit formed jointly by the lig. radiocarpeum palmare and lig. carpi radiatum on the palmar side of the carpus that functions specifically to prevent hyperextension of the carpal joint.

Articulationes intermetacarpeae (eq)

Tight joints with minimal movement between Mc II and Mc III, as well as between Mc IV and Mc III. The proximal aspect of this joint is incorporated into the joint capsule of the articulatio carpometacarpea.

Articulatio metacarpophalangea (fetlock joint, eq)

A composite ginglymus joint between the trochlea of Mc III, the base of the proximal phalanx (Ph1), and the two proximal sesamoid bones. It carries significant weight in a normal position of hyperextension (dorsalflexion) supported by a complex suspensory apparatus.

Recesses of the fetlock joint (eq)

The synovial outpocketings of the articulatio metacarpophalangea consisting of a smaller recessus dorsalis and a larger recessus palmaris.

Musculus interosseus medius (suspensory ligament, eq)

A completely tendinous muscle representing the strongest component of the stay apparatus in horses. Originating from the distal row of carpal bones, carpal palmar ligaments, and bases of metacarpal bones, it inserts onto the proximal sesamoid bones via medial and lateral limbs and gives off the tractus appositus.

Tractus appositus

Two tendinous bands branching from the m. interosseus medius that run obliquely dorsodistally from the medial and lateral sides to join the extensor tendon of the m. extensor digitorum communis.

Ligamentum metacarpointersesamoideum

A proximal sesamoid ligament that arises from the palmar surface of Mc III and inserts onto the palmar ligaments (ligg. palmaria) between the proximal sesamoid bones.

Ligamenta palmaria (fetlock joint)

Transverse fibrocartilaginous fibers running between the proximal sesamoid bones that fuse with them to form the smooth scutum proximale for the digital flexor tendons.

Ligamentum sesamoideum rectum (Y ligament)

A straight distal sesamoid ligament originating from the proximal sesamoid bones. It divides into a superficial part inserting onto the middle phalanx (Ph2) and a deep part inserting onto the proximal phalanx (Ph1).

Ligamenta sesamoidea obliqua (V ligament)

Oblique distal sesamoid ligaments that pass from the bases of the proximal sesamoid bones distally to attach to the triangular area (trigonum phalangis proximalis) on the palmar surface of Ph1.

Ligamenta sesamoidea cruciata (X ligament)

Deep, crossing distal sesamoid ligaments that originate from the bases of the proximal sesamoid bones and cross each other to attach to the proximal palmar border of Ph1.

Ligamenta sesamoidea brevia

Short distal sesamoid ligaments extending directly from the anterior bases of the proximal sesamoid bones to the proximal articular margin of Ph1.

Articulatio interphalangea proximalis manus (pastern joint, eq)

A simple saddle joint (articulatio simplex, articulatio sellaris) between the trochlea of Ph1 and the base of Ph2 that permits extension, flexion, and minimal side movement. It features a dorsal and palmar recess and is reinforced by collateral and palmar ligaments.

Articulatio interphalangea distalis manus (coffin joint, eq)

A composite saddle joint (articulatio composita, articulatio sellaris) between the trochlea of Ph2, Ph3, and the distal sesamoid (os naviculare). It contains a dorsal and palmar recess and is closely associated with the podotrochlear bursa.

Bursa podotrochlearis manus (Brauelli)

A synovial bursa located between the palmar (flexor) surface of the navicular bone (os naviculare) and the terminal portion of the deep digital flexor tendon, found exclusively in ungulates.

Ligamentum sesamoideum distale impar

A short, broad median ligament connecting the distal border of the navicular bone (os sesamoideum distale) directly to the distal phalanx (Ph3).

Ligaments of the cartilago ungularis

The ligamentous apparatus anchoring the hoof cartliages: ligg. chondrocompedalia (to Ph1), ligg. chondrocoronalia (to Ph2), ligg. chondrosesamoidea (to navicular bone), and ligg. chondroungularia collateralia and cruciata (to Ph3).

Ruminant-specific digit ligaments

Four additional interdigital ligaments present in ruminants: 1. Lig. intersesamoideum interdigitale, 2. Lig. phalangosesamoideum interdigitale, 3. Lig. interdigitale proximale, and 4. Lig. interdigitale distale.

Musculus interosseus medius bands (ru)

The fused interosseus muscle in ruminants consisting of: a medial band (attaching to abaxial sesamoid III), a lateral band (to abaxial sesamoid IV), and a middle band dividing into side limbs (3a to axial sesamoids) and an interdigital limb (3b).

Ligamenta dorsalia (ca)

Two elastic ligaments situated dorsally between Ph2 and Ph3 in carnivores that maintain passive retraction of the claws.

Canalis carpi (carpal canal)

A canal bounded dorsally by the proximal row of carpal bones and palmarily by the retinaculum flexorum. It transmits the tendons of the digital flexor muscles, their synovial sheath, as well as nerves and blood vessels.

Digital annular ligaments

Three regional transverse thickenings of the fascia digiti that bind the digital flexor tendons to the palmar aspect of the digit: lig. anulare palmare, lig. anulare digitale proximale (pars cruciformis), and lig. anulare digitale distale (pars anularis).

Musculus extensor carpi radialis (ca)

The strongest extensor of the carpal joint (also minimally flexing the elbow). It originates from the crista epicondyli lateralis humeri and inserts on the bases of Mc II and Mc III dorsally.

Musculus extensor carpi ulnaris (m. ulnaris lateralis, ca)

A muscle originating from the epicondylus lateralis humeri that inserts onto the lateral base of Mc V and the accessory carpal bone. It supports the extended carpus during weight-bearing and aids in flexion, abduction, and lateral rotation.

Musculus flexor carpi radialis (ca)

A carpal flexor muscle originating on the epicondylus medialis humeri (behind the medial collateral ligament) and inserting onto the palmar bases of Mc II and Mc III.

Musculus flexor carpi ulnaris (ca)

A carpal flexor muscle arising by two heads—caput humerale from the epicondylus medialis humeri and caput ulnare proximo-caudally from the ulna—both inserting onto the os carpi accessorium.

Musculus extensor digitorum communis (ca)

A digital extensor arising from the epicondylus lateralis humeri that divides into four tendons inserting onto the processus extensorius of the distal phalanx of digits II–V, extending both the carpus and digital joints.

Musculus extensor digitorum lateralis (ca)

A muscle originating from the lateral humeral epicondyle and lateral collateral ligament that extends the carpus and digits III–V, uniting near the digit level with the common digital extensor tendon and tractus appositus to insert onto Ph3.

Musculus extensor digiti I. et II. (pollicis et indicis, ca)

A muscle originating on the lateral middle third of the ulna. Its pollicis branch inserts on the head of Mc I, while its indicis branch joins the common digital extensor to insert on Ph3 of digit II, functioning to extend digits I–II and adduct the dew claw.

Musculus abductor digiti I. longus (ca)

A muscle originating from the lateral surfaces of the radius, ulna, and interosseous membrane that crosses obliquely to insert on the medial base of Mc I, acting to extend and abduct digit I.

Musculus flexor digitorum superficialis (ca)

A flexor originating from the medial epicondyle of the humerus whose tendons insert on the palmar surface of the middle phalanx of digits II–V. At the level of the fetlock joint, each tendon forms a tubular sleeve called the manica flexoria.

Manica flexoria

A tubular collar or cuff formed by the superficial digital flexor tendon at the fetlock joint level through which the tendon of the deep digital flexor passes.

Musculus flexor digitorum profundus (ca)

The deep digital flexor arising by three heads—caput humerale, caput radiale, and caput ulnare—whose combined tendon passes through the carpal canal and manica flexoria to insert on the palmar surface of the distal phalanx of digits I–V.

Musculus pronator teres (ca)

A pronator muscle running from the epicondylus medialis humeri to the craniomedial surface of the upper radius that rotates the forearm medially.

Musculus pronator quadratus (ca)

A muscle filling the interosseous space medially between the apposed surfaces of the radius and ulna whose fibers run transversely to pronate the forearm.

Musculus supinator (m. supinator brevis, ca)

A supinator muscle arising from the lateral epicondyle of the humerus and the lateral collateral ligament that inserts on the cranial surface of the proximal radius to rotate the forearm laterally.

Musculus brachioradialis (m. supinator longus, ca)

A supinator present in approximately $33\%$ of dogs that originates from the crista supracondylaris humeri and inserts distomedially on the radius.

Muscle of Thiernesse (eq)

The accessory head (caput accessorium) of the m. extensor digitorum communis in the horse, originating from the ulna.

Muscle of Phillips (eq)

The accessory head (caput accessorium) of the m. extensor digitorum lateralis in horses, arising from the m. extensor digitorum communis and inserting onto Ph1.

Proximal check ligament (ligamentum accessorium of MFDS, eq)

A reinforcing fibrous band extending from the distal caudomedial aspect of the radius to the superficial digital flexor tendon, functioning as an integral part of the passive stay apparatus.

Distal check ligament (ligamentum accessorium of MFDP, eq)

A reinforcing ligament that represents the direct fibrous continuation of the lig. carpi palmare profundum, joining the deep digital flexor tendon to support the stay apparatus.

Vagina synovialis communis musculi flexorum (eq)

The upper common flexor tendon sheath found only in horses, enclosing the superficial and deep digital flexor tendons within the carpal canal (fixed by the retinaculum flexorum) and extending proximal and distal to the carpus.

Vagina synovialis tendinum digitorum manus

The lower common digital flexor tendon sheath present in all domestic species, enclosing both digital flexor tendons at and distal to the fetlock joint within the manica flexoria.

Scuta (scutum proximale, medium, and distale, eq)

Three smooth fibrocartilaginous pads on the palmar surface of the digit: scutum proximale (proximal sesamoids and lig. palmare), scutum medium (palmar Ph2 statumen), and scutum distale (palmar navicular bone for the MFDP tendon only).

Passive stay apparatus (eq)

A specialized system of tendons, ligaments, and transformed muscles (including the lacertus fibrosus, check ligaments, suspensory apparatus, and tractus appositus) that lock major limb joints, enabling horses to stand for long periods and sleep while standing with minimal muscular effort.