-----------------------+-----------------------+----------------------- MAN. | DOG. | HORSE. -----------------------+-----------------------+----------------------- A. Long abductor of the|A. Long abductor of the|A. _Oblique extensor of of the thumb, and | thumb and short | the metacarpus_, the short extensor of | extensor of the | homologue of the the thumb. | thumb united as one | long abductor of the | muscle, _the oblique| thumb and the short | extensor of the | extensor of the | metacarpus_.[11] | thumb, united as one | | muscle. | | B. First and second |B. The two radials |B. The radials external radials | blended superiorly, | represented by a (_extensor carpi | distinct inferiorly;| single muscle, _the radialis longior_ | this is _the | anterior extensor of and _brevior_). | anterior extensor of| the metacarpus_. | the metacarpus_. | | | C. Long extensor of the|C. Long extensor of the|C. The long extensor of thumb. | thumb and special | the thumb and the | extensor of the | special extensor of | index finger united | the index are | superiorly. These | absent. | muscles pass in the | | following groove. | | | D. Special extensor of |D. Common extensor of |D. _Anterior extensor the index finger and| the digits and the | of the phalanges_, the common extensor | two preceding | the homologue of the of the fingers. | muscles. | common extensor of | | the digits. | | E. Special extensor of |E. _Extensor of the |E. Lateral extensor of the little finger. | third, fourth, and | the phalanges, the | fifth digits_, or | homologue of the | _the lateral | special extensor of | extensor of the | the little finger. | digits_, the | | homologue of the | | special extensor of | | the little finger. | | | F. The posterior ulnar |There does not exist on the forearm a groove (_extensor carpi |for the posterior ulnar muscle, or _external ulnaris_). |flexor of the metacarpus_. -----------------------+-----------------------------------------------
[11] The words printed in italics are the names used in veterinary anatomy.
It is also useful to note, with reference to the groove F, in which passes, in man, the tendon of the posterior ulnar muscle, that, when the forearm is in pronation, the radius alone being displaced, we can only see this groove on the surface which looks backwards; and that it is then separated from the groove which contains the tendon of the special extensor of the little finger by an interval equal to the thickness of the head of the ulna.[12] When the forearm is supinated, the two grooves are found, on the other hand, one beside the other: and the tendons which they contain are very naturally in contact.