The =extensor carpi radialis= is a strong, fleshy muscle, the tendon of
which is inserted into the proximal end of the third metacarpal bone. It
may be divided into two parts (M. extensor carpi radialis longus,
brevis).
The =extensor carpi obliquus= is well developed; it ends on the second
metacarpal bone.
There are three (or four) =digital extensors=.
1. The =common= or =anterior digital extensor= (M. extensor digitalis
communis) arises on the extensor epicondyle of the humerus and the
lateral ligament of the elbow, and divides into three parts. The tendon
of the =inner part= divides into two branches which end on the =second=
and =third digits=; the tendon to the second digit is small and often
absent. The tendon of the =middle part= divides lower down into two
branches for the =third= and =fourth= (chief) =digits=; above this
bifurcation it detaches a small branch to the =second digit=, which
usually unites with the tendon of the extensor indicis. The tendon of
the =deep head= divides into two branches, the inner one joining the
tendon of the middle head, while the outer one ends on the =fifth
digit=.
[Illustration:
FIG. 227.—MUSCLES OF ANTIBRACHIUM AND MANUS OF PIG, ANTERO-EXTERNAL
VIEW.
_a_, _a′_, Extensor carpi radialis; _b_, extensor carpi obliquus (s.
abductor pollicis longus); _c_, _d_, _e_, common or anterior digital
extensor; _c′_, _c″_, tendons of insertion of _c_; _d′_, _d″_,
tendons of _d_; _e′_, _e″_, tendons of _e_; _f_, tendon of extensor
indicis; _g_, extensor digiti quarti; _h_, extensor digiti quinti;
_h′_, tendon of _h_; _i_, tendinous, and _k_, fleshy part of flexor
carpi externus; _k′_, tendon of _k_; _l_, ulnar head of deep digital
flexor; _m_, superficial digital flexor; _n_, brachialis. (After
Ellenberger, in Leisering’s Atlas.)
]
2. The =extensor of the second digit= (M. extensor indicis proprius) is
covered by the preceding muscle, with which it is partially fused. It
arises on the ulna. Its delicate tendon usually unites with the tendon
of the middle head of the common extensor which goes to the =second
digit=.
3. The =lateral digital extensor= (M. extensor digitalis lateralis)
consists of two distinct parts: (1) The large =dorsal= (anterior)
=muscle= (M. extensor digiti quarti proprius) has a long tendon which
ends on the =fourth digit=, and often sends a slip to the fifth digit.
(2) The small =volar= (posterior) =muscle= (M. extensor digiti quinti
proprius) ends by a long tendon on the lateral aspect of the =fifth
digit=.
The =supinator= has been found by Arloing and Lesbre, but is usually
absent in the pig.
The =pronator teres= is a small muscle which lies on the internal
lateral ligament of the elbow. It arises from the internal epicondyle of
the humerus, and reaches about to the middle of the inner border of the
radius.
The =flexor carpi internus= is well developed. It arises on the flexor
epicondyle of the humerus, and is inserted into the third metacarpal
bone.
The =flexor carpi medius= is narrow and has no ulnar head.
The =flexor carpi externus= (M. extensor carpi ulnaris) is covered by a
thick, tendinous band, which extends from the extensor epicondyle to the
accessory carpal bone and outer aspect of the carpus. The tendon of the
muscle perforates this band in the distal part of the forearm and ends
on the proximal end of the fifth metacarpal bone.
The =superficial digital flexor= has two bellies. The tendon of the
=superficial head= passes down behind the posterior annular ligament of
the carpus (bound down by a special annular ligament), forms a ring at
the fetlock for a tendon of the deep flexor, and ends by two branches on
the second phalanx of the =fourth digit=. The tendon of the =deep head=,
after detaching a slip to the tendon of the deep flexor, passes down
with the latter (for which it forms a ring), and ends on the =third
digit=.
The =deep digital flexor= has three heads—humeral, ulnar, and radial.
The common tendon divides into four branches, the larger central pair
ending on the third phalanges of the principal digits, the smaller pair
on the accessory digits. The latter are bound down by a peculiar spiral
band. There is no check ligament.
The =lumbricales= are represented by bundles which extend from the deep
flexor tendon to the tendon of the deep head of the superficial flexor.
The third and fourth =interossei= are present. Each sends two slips to
the corresponding sesamoid bones and extensor tendon.
There are =flexors=, =adductors=, and =abductors= of the =second= and
=fifth digits=.