Myology and Serology of the Avian Family Fringillidae: A Taxonomic Study

by William B. Stallcup

Action.—Flexes digit II.

Comparison.—In Passer, Estrilda, Poephila, Hesperiphona, Carpodacus, Pinicola, Leucosticte, Spinus, and Loxia the proximal portion of this muscle is more intimately connected with the posterior edge of the m. flexor perforans et perforatus digiti III than it is in the other species examined.

Musculus flexor perforans et perforatus digiti III (Fig.[ 2]).—Long and pinnate, this muscle lies on the lateral surface of the crus beneath the m. peroneus longus and pars externa of the m. gastrocnemius. There are two distinct heads. The origin of the anterior head is fleshy from the proximal edge of the outer cnemial crest and from the internal edge of the distal end of the patellar tendon. The posterior head arises by a tendon from the femur in company with the m. flexor perforans et perforatus digiti II, is connected also with the tendon of origin of the m. flexor perforatus digiti II, and is loosely attached to the head of the fibula. Fibers from the belly of the muscle attach throughout its length to the lateral edge of the fibula, and the muscle is tightly fused also with adjacent muscles. The tendon of insertion is formed approximately one-half the way down the crus. The tendon perforates the posterior surface of the tibial cartilage and passes through the posteromedial canal of the hypotarsus (Fig.[ 6]). At the base of the third digit the tendon ensheathes that of the m. flexor digitorum longus and the two together perforate the tendon of the m. flexor perforatus digiti III. Immediately distal to this perforation the tendon of the m. flexor perforans et perforatus digiti III ceases to ensheath that of the m. flexor digitorum longus. The latter passes beneath that of the former. Near the distal end of the second phalanx the tendon of the m. flexor digitorum longus perforates that of the m. flexor perforans et perforatus digiti III. The latter inserts on the posterior surface of the distal end of the second phalanx and the proximal end of the third.

Action.—Flexes digit III.

Comparison.—In Passer, Estrilda, and Poephila, and in all the cardueline finches examined the proximal portion of this muscle is more intimately connected with the anterior edge of the m. flexor perforans et perforatus digiti II than it is in the other species examined.

Musculus flexor digitorum longus (Figs.[ 3],[ 5]).—This strong, pinnate muscle is deeply situated along the posterior surfaces of the tibia and fibula. There are two distinct heads of origin. The lateral head arises by means of fleshy fibers from the posterior edge of the head of the fibula. The medial head arises by means of fleshy fibers from the region under the ledgelike external and internal articular surfaces of the proximal end of the tibia. Neither head has any connection with the femur in contrast to the condition, described by Hudson (1937: 46-47) in the crow, Corvus brachyrhynchos, and in the raven, Corvus corax. Near the point of insertion of the m. biceps femoris the two heads fuse. The common belly is attached by fleshy fibers to the posterior surface of the tibia and fibula for two-thirds of the distance down the crus. Near the distal end of the crus the muscle terminates in a strong tendon which passes deeply through the tibial cartilage and traverses the anteromedial canal of the hypotarsus (Fig.[ 6]). About midway down the tarsometatarsus this tendon becomes ossified. Immediately above the bases of the toes it gives rise to three branches, one to the posterior surface of each of the foretoes. These branches perforate the other flexor muscles of the toes as described in the accounts of those muscles and insert as follows: The branch to digit II inserts on the base of the ungual phalanx and by a stout, tendinous slip on the distal end of the second phalanx (Fig.[ 9]). The branch to digit III inserts on the base of the distal end of the third phalanx and a stronger slip to the distal end of the second or proximal end of the third. The branch to digit IV inserts on the base of the ungual phalanx, with one tendinous slip to the distal end of the third phalanx and another to the distal end of the fourth.

Action.—Flexes foretoes.

Comparison.—No significant differences noted among the species studied.

Musculus flexor hallucis longus (Fig.[ 3]).—Situated immediately posterior to the m. flexor digitorum longus, the belly of this large, pinnate muscle is intimately connected anteriorly to that of the m. flexor perforatus digiti II. The m. flexor hallucis longus arises by two heads which are separated by the tendon of insertion of the m. biceps femoris. The smaller anterior head arises from the same tendon as does the m. flexor perforatus digiti II. The larger posterior head arises by means of fleshy fibers from the intercondyloid region of the posterior surface of the femur along with the m. flexor perforatus digiti III and IV. The two heads join just distal to the point of insertion of the m. biceps femoris. There is no trace of a tendinous band connecting the two heads as there is in the crow and in the raven (Hudson, 1937:49). Near the distal end of the shank the muscle gives rise to a strong tendon which perforates the tibial cartilage along its lateral edge and passes through the anterolateral canal of the hypotarsus (Fig.[ 6]). The tendon crosses over to the medial surface of the tarsometatarsus, passes distally, and perforates the sheathlike tendon of the m. flexor hallucis brevis between the first metatarsal and the trochlea for digit II. The tendon continues along the posterior surface of the hallux and has a double insertion; the main tendon attaches to the base of the ungual phalanx and a smaller branch inserts on the distal end of the proximal phalanx.

Action.—Flexes hallux.