The rudimentary hind limbs of the sperm whale physeter macrocephalus its variability and allometry of growth
Zeitschrift fuer Saeugetierkunde 42(2): 88-101
The hind limbs of both the Mystacoceti and Odontoceti are fairly equally reduced. The 2 relatively small rudimentary pelvic bones are suspended in muscle unattached to the vertebral column, one on each side of the urogenital tract. Their size and shape are unusually variable. Generally the pelvic bones of the Odontoceti are more reduced than those of the Mystacoceti, whereas the rudiment of the sperm whale sometimes shows a similarity of form to the pelvis of the Mystacoceti. This configuration allows for classification (ilium, ischium, pubig). In many cases the pubis can be seen clearly but it is always the most reduced of the 3 elements. In the reference bone material there is no trace of an acetabulum. Sometimes femur rudiments are found, mostly near the hind end, porously ossified or just cartilaginous. There appears to be no configuration difference between males and females. In spite of a certain variability there is an obvious relation between the body and pelvic bone length. Whereas the bones of males show a negative allometri or almost isometric growth, those of the females seem to increase more rapidly and display positive allometry. In the early embryological phase external hind limbs exist which recede before the skeleton begins to form. After the 1st anlage of the hind limbs, there seems to be an early rudimentation because of an obviously negative allometric growth. There must be positive allometric growth during the late embryonic or postembryonic stage.