(C) The Anatomy of Apes (cont.)
Ape Skeleton - Appendicular Skeleton (cont.): Pelvic Limbs; Ilium; Ischium; Femur; Tibia; Fibula.
The entire pelvic limb, measured from the summit of the femur to the distal end of the longest digit, is absolutely greatest in the gorilla, and then in the orang and the chimpanzee. If the pes be removed, then the leg of the chimpanzee is longer than that of the orang.
Compared with the length of the spine, the entire pelvic limbs of Hylobates and Ateles are longest, namely, as 162 or 169 to 100. That of Hapale is the shortest, being but as 110 to 100. Without the pes, the leg of Hapale is also shortest relatively compared with the spine, namely, as 77 to 100; while that of Hylobates is longest, namely, as 125 to 100.
The os innominatum is in every species strikingly different in form from that of man. In absolute size this bone attains its maximum in the gorilla, where it is much larger than in man, and where the ilium is very broad. The external surface of the ilium is generally more or less concave, and concave only. In Troglodytes and Simia, however, it is more or less convex, but not as in man, and therefore there is no sigmoid curvature of the crest of the ilium, and there are no distinct gluteal lines. The internal surface of the ilium is generally narrow and flat, or only slightly concave, except in the gorilla. The tuberosity of the ischium is always a marked and more or less rugose enlargement of the bone; but in the Simiadae below Troglodytes it is flattened and very much developed, and so much everted that sometimes (in Cynocephalus) its transverse exceeds its antero-posterior diameter. In the Cebidae it again becomes small, and more or less rounded.
The spine of the ischium is generally very small, yet distinct. Only in Simia does it attain a considerable sharpness and prominence. The great sciatic notch is never very deep and concave, as in man. It is most concave in the gorilla, the orang, and in Cynocephalus. The lesser sciatic notch is generally represented by a margin which is so slightly concave as to be almost or quite straight save through the eversion of the tuberosity. The projection of the spine of the ischium produces in man a deep notch such as exists in no ape. The cotyloid notch, and the excavation continuous with it, are constantly present, even in Simia, where, however, it is very small and narrow, in harmony with the absence of the ligamentum teres.
The femur's length, compared with that of the spine, is as 67 to 100 in Hylobates, 61 in Ateles, 54 in the gorilla 47 in Simia. It is shortest in Chrysothrix, 40, and Hapale, 37. In the Simiinae it is shorter than in the humerus, its proportion to which in Simia is as 73 to 100. only in some of the Semnopithecinae does its length exceed that of the humerus more than it does in man. The shaft of the femur is sometimes nearly straight, as in Hylobates and in most Cebidae. The femur is stoutest, relatively as well as absolutely, in the gorilla. It is slendered in Hylobates. The neck of thefemur is longest in Simia and Hylobates; shortest in Hapale. Except in the Simiinae and in Mycetes, the great trochanter is pointed at its upper end. The trochanteric fossa is shallow in the gorilla, but is in most forms deep. The lesser trochanter is at its minimum of relative size in the Simiinae, and is largest relatively in Hapale, and the posterior surface of the femur is in that genus wide and flat between the trochanters. The pit for the insertion of the ligamentum teres is always present, except in the orang and gorilla, where it is absent almost constantly in the first ape, occasionally in the second. In the Simiinae, Ateles, and Lagothrix the internal condyle projects considerably further backwards than does the external one. The angle formed by the neck of the femur with the shaft varies from about 155° (Simia) to 128° (the gorilla)
The tibia and fibula never become ankylosed together. The tibia is absolutely longest in the gorilla. Its length, compared with that of the spine, is never so great as in man, except in Hylobates, in which it is slightly longer relatively. It is shortest in Mycetes, about as 37 to 100. its length is generally less than that of the femur, but sometimes, in Hapale, it slightly exceeds it. It is never, however, so short compared with the femur as in man. The crest of the tibia is not so sharp as in man. The shaft is sometimes straight, as in Lagothrix and Pithecia, sometimes considerably curved, as in the gorilla and lower Cebidae. The malleolus is generally well-developed, but sometimes, as in the orang, very short. Its articular surface is sometimes nearly at right angles with the inferior surface of the shaft of the tibia, as in the chimpanzee; sometimes it forms an obtuse angle with that surface, as in the gorilla, and still more in the orang. The distal articular surface of the shaft of the tibia is rarely horizontal, as in Ateles and Lagothrix. In the Simiadae and lower Cebidae the outer portion rises so that the articular surfacr slopes upwards peronead. The fibula has its malleolus much produced outwards, projecting only about as much as, or rather less than, the tibial malleolus, whereas in man the fibular malleolus is much deeper than the tibial one.
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