Mm. flexores breves

WHIDDEN, HOWARD P., 2000, Comparative Myology of Moles and the Phylogeny of the Talpidae (Mammalia, Lipotyphla), American Museum Novitates 3294, pp. 1-53 : 41-42

Mm. flexores breves ( fig. 19 )

In Uropsilus , there is a medial and a lateral M. flexor brevis for each digit. The muscles

for digits I and V originate from tiny sesamoids at the proximal ends of their respective metatarsals, whereas the muscles for the other digits originate from connective tissue over the tarso­metatarsal joints. Insertion is on paired sesamoids that lie on either side of the plantar surfaces of the metatarso­phalangeal joints. Neurotrichus , Scaptonyx , and Urotrichus also have paired muscles for each digit. These muscles originate from the proximal ends of the metatarsals and from connective tissue over the tarso­metatarsal joints, and they insert on the sides of the metatarsophalangeal sesamoids. In these genera, and in all talpids other than Uropsilus , the metatarso­phalangeal sesamoids are single, and the flexor muscles insert on their respective sides of the sesamoid. Desmana and Galemys are similar to Uropsilus except that the medial flexor for digit I originates from the proximal end of the first metatarsal, and the lateral flexor for this digit is absent. In the remaining taxa there are fewer of these muscles. They originate from connective tissue at the base of the metatarsals, and the tendons of insertion continue past the metatarsophalangeal sesamoids and wrap around the sides of the digits to insert on a sesamoid on the dorsal surface of the first phalanx. Condylura has paired muscles for digits II and III and a medial muscle for digit IV. Parascalops has paired muscles for digits II and III and medial muscles for digits IV and V. Talpa has paired muscles for digits II, III, and IV. Scalopus and Scapanus have paired muscles for digits II and III and a medial muscle for digit IV.

REMARKS: I could not determine if the tendons of insertion extended to the dorsal surface of the digits in Desmana , Galemys , Neurotrichus , Scaptonyx , and Urotrichus . Also, there may be intraspecific variability in these muscles, as one of the specimens of Scapanus that I dissected also had a lateral muscle for digit IV and a medial muscle for digit V, and I could not find the medial muscle for digit V in some specimens of Parascalops . However, these are tiny muscles, and observational error or nongenetic factors (such as method of preservation or condition of specimens at the time of preservation) could explain the variability. Reed (1951) reported that Neurotrichus had three Mm. flexores breves per digit, but I believe that he confused a tendon that extends from the plantar connective tissue to the metatarso­phalangeal sesamoid of each digit for a third M. flexor brevis .

Figures

Fig. 19. Intrinsic muscles of the pes of Neurotrichus.