. Chordate morphology. Morphology (Animals); Chordata. poir of sesamoids under each joint at this level Q lateral intermedial medial cuneiform pisiforme epiphysis A C B Figure 6-46. Manus, A and B, and pes, C and D, of man and the opossurr. cuboid calcaneus fibula and the (ventroanterior) pubis (Figure 6-47). Where these elements come together, there is a deep socket, the acetabu- lum, into which fits the head of the basal limb bone, the femur. The pubis and ischium are partly separated by a large round obturator foramen. The form of the pelvic girdle of the cat and the opossum is very similar
. Chordate morphology. Morphology (Animals); Chordata. poir of sesamoids under each joint at this level Q lateral intermedial medial cuneiform pisiforme epiphysis A C B Figure 6-46. Manus, A and B, and pes, C and D, of man and the opossurr. cuboid calcaneus fibula and the (ventroanterior) pubis (Figure 6-47). Where these elements come together, there is a deep socket, the acetabu- lum, into which fits the head of the basal limb bone, the femur. The pubis and ischium are partly separated by a large round obturator foramen. The form of the pelvic girdle of the cat and the opossum is very similar except that in the opos- sum the suture lines between the elements are evident. In addition, there is a bone, the marsupial bone, which extends forward from the anterior margin of the pubis. This bone appears to support the body wall and the marsupium, the pouch in which the young are suckled. In the monotreme the pelvis is similar to that of the mar- supial. Presence of the marsupial bone in these two groups suggests its presence in their common ancestor, although such a bone is not known in the therapsids. It therefore ap- pears to be a neomorph, and perhaps is an independently ac- quired parallelism in the two groups—a slight marsupial fold is observed in the female Echidna. The pelvic limb, like the pectoral, has basal stylopodial, middle zeugopodial, and distal autopodial segments. The basal element in the thigh (stylopodium) is the femur, while the tibia and fibula form the middle segment or shank, the zeugopodium. The autopodium is subdivisible into a basal series of tarsals, the basopodium, a series of metatar- sals in the metopodium, and the digits which form the acropodium. The names applied to the various tarsals are indicated in Table 6-3. The pelvic limb is remarkably constant in its elements. The foot of the opossum or monotreme is much like that of man, and there is also close agreement in their epiphyses. Again, as in the forelimb, the second to fifth metatar
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