metacarpal bone of the middle finger, sending a few fibres to those of the index and ring fingers. In two specimens dissected by Duvernoy, he found this muscle performing the office of an Extensor proprius of the middle finger only, and in another specimen it was inserted into both the index and middle fingers; see also Cuvier, l.c. pl. 17.
In the Gorilla, according to Duvernoy (p. 97), it goes to the index only, but it is very weak. In the Chimpanzee, according to Vrolik, the tendinous insertion is confined to the index, but the muscle at its origin appears to be fused with the common Extensor. In an Ateles I found it to terminate by two distinct tendons; one of which was inserted into the index and radial side of the middle finger, the other into the ulnar side of the middle and the ring finger. In the Cebus and Magot, the two tendons were inserted severally into the middle and index fingers.[1]
The extensor muscles in the human subject are very liable to variations, and the commonest resemble those arrangements found normally in the Quadrumana. Mr. Hallett says of the Extensor Minimi Digiti, "it is occasionally absent, being replaced by the Extensor Communis; more frequently split into two tendons, or two muscles even, going to the ring and little fingers." The sending off of a slip to join the tendon of Extensor Communis going to the ring finger is described by Vesalius.[2] Theile[3] mentions the same arrangement as Mr. Hallett. Mr. Hallett also describes a case in which the Extensor Indicis was divided into two distinct muscles, the tendon of one of them going to unite with the index branch of the common extensor, while the other went to the middle finger: this was the most complete irregularity met with, but many minor grades were noticed. Theile[4] mentions the tendon being double, a branch going to the middle finger.[5]
The want of specialization of this muscle in the Orang must be regarded as a lower organization than that of the Chimpanzee or Gorilla, which, from their myology, I should think are able to point with their finger in the same manner as man.
The Pronator Teres, Flexor Carpi Radialis, Palmaris Longus, and Flexor Carpi Unaris presented the closest resemblance to the same muscles in man. But the individuality of the several muscles was less marked; they appeared to have a common origin from the inner condyle of the humerus and intermuscular septum, and owing to the interlacement of their fibres, none of the muscles could be traced out to their individual origins. The same remarks apply to these muscles in the Magot and Cebus.
The Flexor Sublimis Digitorum. The portion of this muscle
- ↑ The muscles known as Extensores primi intermodii pollicis, Indicis and Minimi digiti, appear to be mere isolated remnants of the complete second or deep extensor digitorum found under various forms in the lower Mammalia.—[Eds.]
- ↑ Vesalii Opera, vol. i. p. 258.
- ↑ Encyc. Anat. tom. iii. p. 230.
- ↑ Wagner, Elements of Comp. Anatomy, translated by Tulk, p. 19.
- ↑ And sometimes this muscle is double and its deeper division gives three tendons, to the 2nd, 3rd and 4th fingers. See Henle, l.c., p. 213.
