The =extensor carpi radialis= is like that of the horse. There is
sometimes a small muscle lying along its inner border, which may
represent the extensores pollicis.
There are three =digital extensors=: 1. The =common= or =anterior
digital extensor= (M. extensor digitalis communis) arises by two heads
from the extensor epicondyle and the ulna. The heads fuse about the
middle of the forearm, and terminate soon on a tendon which passes over
the carpus and metacarpus, gradually inclining forward. At the fetlock
joint it divides into two branches, which are inserted into the third
phalanges. 2. The =internal digital extensor= (M. extensor digiti tertii
proprius) arises on the extensor epicondyle, and is inserted by two
branches into the second and third phalanges of the inner digit. The
tendon receives two reinforcing slips from the suspensory ligament. 3.
The =lateral digital extensor= (M. extensor digitalis lateralis s.
digiti quarti proprius) arises from the external lateral ligament of the
elbow joint, the external tuberosity of the radius, and the ulna. The
tendon terminates like that of the preceding muscle.
[Illustration:
FIG. 215.—RIGHT CARPUS OF OX WITH BURSÆ AND SYNOVIAL SHEATHS INJECTED,
EXTERNAL VIEW.
]
[Illustration:
FIG. 216.—RIGHT CARPUS OF OX WITH BURSÆ AND SYNOVIAL SHEATHS INJECTED,
INTERNAL VIEW.
_1_, Extensor carpi radialis, with synovial sheath (_1′_) and bursa
(_1″_); _2_, extensor carpi obliquus, with synovial sheath (_2′_)
and bursa (_2″_); _3_, extensor digiti tertii proprius; _4_,
extensor digitalis communis; _3′_, common synovial sheath of _3_ and
_4_; _5_, extensor digiti quarti proprius, with synovial sheath
(_5′_); _6_, _6′_, flexor carpi externus, with bursa (_6″_); _7_,
flexor carpi internus, with synovial sheath; _8_, deep digital
flexor, with synovial sheath (_8′_); _9_, flexor carpi medius; _10_,
superficial digital flexor, with synovial sheath _10′_; _a_, radius;
_b_, carpus; _c_, metacarpus; _d_, cut edge of annular ligament.
(After Schmidtchen.)
]
The =extensor carpi obliquus= resembles that of the horse.
The extensor tendons are bound down at the carpus by an annular
ligament, and are furnished with synovial sheaths (Figs. 215, 216).