In the immature Batrachian a triangular shaped cartilage intervenes between the op posing ilia and the other pelvic bones in the acetabula, which afterwards becomes oblite rated by the ankylosis of the bones. Duges calls it an " os paracotyleal," analogous to the " paraglenal" bone of the shoulder of the same animal. There are also epiphysial pieces on the ilia and ischia which represent the crest and tuberosity of those bones respectively.
The solidity and firmness of union of the ischio.pubic portion of the pelvis in the frog is a remarkable instance of modification and adaptation of form to meet the requirements for a strong and firm hold for the powerful triceps cruris, external obturator, hamstring, and:ad ductor muscles in the thigh of this animal. The single pair of glutei also obtain an ex tensive attachment from the long ilia, and the pyriformes from the long coccygeal spine, while the strong abdominal niuscles, acting on the moveable ilia, give, as it were, an additional segment to the hinder extremities. In this manner the frog's pelvis is strikingly and di rectly adapted to its leaping progression.
In the Fishes the pelvic structures dwindle to elementary pieces, such as we have. men tioned in the bimanal and apodal Reptiles, and finally disappear altogether.
The pelvis is represented in these animals by two bones, sometimes coalesced into an azygos bone, which support the ventral fins. In the Pisces thoracici these are suspended by ligament to the coracoids, by which they are advanced anterior to the pectoral fins, and connected to the head ; but in the Pisces abdominales they are detached from the coracoids, and are suspended in the muscles at the posterior part of the ab domen. They are, however, subject to great diversity of position.
Owen considers the pelvic bones of fishes to be the homologues of the pubes ; but, in the opinion of Carus, they are to be considered as ilia. Their inferior and ventral position, their occasional union in a symphysis, their frequent coalescence, and their attachment to the generative organs, however, would support rather the conclusion of Professor Owen ; the support of the bones of the extretnities not being exclusively the iliac attribute, but also usually contributed to by the pubes and ischia. In Fishes, a supporting arch from the spinal column to the posterior limbs* is not wanted, but rather a free and unimpeded motion for the caudal extremity, used in propelling the body.
In the Angler there are two pelvic bones, each consisting of a vertical portion,,which, in this instance, seems to represent the ilium, and a horizontal ,one, which meets in a symphysis with the one on the opposite side, and is the homologue of the pubis, the pectoral ra3 s being attached to the angle of union of the two portions. In the Rays and Sharks, where the pelvic extremities are better de veloped than in other fishes, the pelvic bones consist of one piece, placed transversely, resembling that which supports the pectoral fins, and suspended loosely, like it, by a ligament to the spine. In the Sharks and
Chimerce are found, articulated to it, by means of an intermediate cartilage, two club-shaped bones, called claspers, which are used to em brace the female in the generative act. In the Torpedo, and also in the Cyclobates oligo dactylus, an extinct Ray, the pubic bone sends forw ard two processes, somewhat resembling marsupial bones. In the Sturgeon, the pelvic bones are almost entirely separated from each other, and consist of small triangular pieces, with their apices directed forwards, and sup portim. the cartilaginous fin ra3s. In the Cod-fish there are two sub-triangular bifur cated bones, connected to each other by liga rnent, and suspended from the coracoids, the rays of the ventral fins springing directly- from them. In the Trout, the pelvic bones are also two in number, flat and Of an elongated angular shape, with the base directed pos teriorly, and supporting the ventral fins (see ,fig. 111. c). In the Haddock, there is a single bone, presenting a central oval opening with the shorter diameter transverse. In the Cyprinus, Scomber, and Zeus, they present backward spinous projections. In theRnombus and Lwicaria there is seen an ankylosis of the anterior caudal vertebrze, forming a sort of sacrum, and presenting the first indication of the formation of this bone in the animal k ingdom.
Subjoined is a table, showing the compara tive pelvic angles in Alan and the principal genera of Mammalia, Birds, and Reptiles. The measurements were principally taken, with great care to insure correctness, from the specimens in the Hunterian 'Museum, through the kindness of Professor Owen. The rela tive size or total disappearance of the verte bro-iliac, sarro-vertebral, and the ilio-pubic and ilio-ischial angles in the different tribes, will be here seen at one view. It may be observed that the two former may vary some what through inaccuracies in articulating the skeleton, or with the variations of the ver tebral curve, and that the results here given are to be taken in this particular, as approxi mative only. But the ilio-pubic and ischial angles cannot, from the ossific union of the bones, be subject to such accidental variations.
The accompanying diagram is intended to show the absolute lines of direction or axes of the pelvic bones and spine seen in profile, with the angles above referred to, in the prin cipal pelvic types.
Having thus taken a general review of the progressive development of the pelvis, and traced it from its most perfect form in man to its most rudimentary elements in the fishes; we can enter more prepared into the consi deration of the serial homologies of the pelvis and its ligaments.