. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 284 MARSUPIALIA. Fig. 110. fetuses that we ought to find auxiliary parts for increasing the power of the muscles engaged in parturition. The bones in question are, moreover, equally developed in both sexes: and they are so situated and attached that they add to the power of the muscles which wind round them, and not of those implanted in then). They are not, however, merely sub- servient to add force to the action of the " cre- masteres," but give origin to a great proportion of the so-called " pyramidales
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 284 MARSUPIALIA. Fig. 110. fetuses that we ought to find auxiliary parts for increasing the power of the muscles engaged in parturition. The bones in question are, moreover, equally developed in both sexes: and they are so situated and attached that they add to the power of the muscles which wind round them, and not of those implanted in then). They are not, however, merely sub- servient to add force to the action of the " cre- masteres," but give origin to a great proportion of the so-called " ; The osteogencsis of the marsupial pelvis de- rives some extrinsic interest from the not yet forgotten speculations which have been broached regarding the analogies of the marsupial bones. These have been conjectured to exist in many of the placental Mammalia, with a certain la- titude of altered place and form, disguised, e. g. as the bone of the penis in the Carnivora, or appearing as the supplemental ossicles of the acetabulum, which exist in the young of many of the Rodentia. In the os innomina- tum of the immature Potoroo the curved pris- matic ilium contributes to form, by the outer part of its base, the upper or anterior third of the acetabulum; the rest of the circumference of this cavity is completed by the ischium and pubis, excepting a small part of the under or mesial margin, which is formed by a distinct ossicle or epiphysis of the ilium, (a, jig. 110,) antilogous to that de- scribed by Geoffrey St. Hilaireastherudimen- tal marsupial bone in the rabbit. Now here there is a co-existing marsupial bone: but besides the five sepa- rate bones just men- tioned, there is a sixth distinct triangular ossi- cle, which is wedged into the posterior in- terspace of the ischio- pubicsymphysis. How easy were it to suggest that this single sym- metrical bone may be the representative of the os penis removed from the glans to the root of the intromittent organ ! 1 regard it
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