Comparison.—Study of the pars externa and pars media reveals no significant differences among the species dissected. The pars interna, however, is subject to some variation which is described below.
Pars interna bipartite
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Vireo Seiurus Icterus Molothrus Piranga Richmondena Guiraca Passerina Spiza |
Chlorura Pipilo Calamospiza Chondestes Junco Spizella Zonotrichia Passerella Calcarius |
The two parts of the m. gastrocnemius are most distinct in Vireo. Icterus, Molothrus, Richmondena, Guiraca, and Passerina lack the fibrous band that passes around the front of the knee. In Spiza this band of fibers is smaller than in the other species.
Pars interna undivided
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Passer Estrilda Poephila Hesperiphona Carpodacus |
Pinicola Leucosticte Spinus Loxia |
In Leucosticte, although the pars interna is undivided, there is a band of fibers which extends around the front of the knee (see discussion, p.[ 183]).
Musculus plantaris (Fig.[ 5]).—Small and slender, this muscle lies on the posteromedial surface of the crus, beneath the pars interna of the m. gastrocnemius and originates by fleshy fibers from the posteromedial surface of the proximal end of the tibia immediately distal to the internal articular surface. The belly extends approximately one-sixth of the way down the crus and gives rise to a long, slender tendon that inserts on the proximomedial edge of the tibial cartilage.
Action.—Extends tarsometatarsus.
Comparison.—No significant differences noted among the species studied.