No interclavicle is present in Urodela, but in this group and in a number of the Anura, a process grows out from the end of each of the bars (præcoracoids) which Götte holds to be the clavicles. The two processes unite in the median line, and give rise in front to the anterior unpaired element of the shoulder girdle (omosternum of Parker). They sometimes overlap the epicoracoids behind, and fusing with them bind them together in the median line. Parker who has described the paired origin of the so-called omosternum, holds that it is not homologous with the interclavicle, but compares it with his omosternum in Mammals.
Bibliography.
(463) Bruch. “Ueber die Entwicklung der Clavicula und die Farbe des Blutes.” Zeit. f. wiss. Zool., iv. 1853.
(464) A. Dugès. “Recherches sur l'ostéologie et la myologie des Batraciens à leurs différens âges.” Mémoires des savants étrang. Académie royale des sciences de l'institut de France, Vol. VI. 1835.
(465) C. Gegenbaur. Untersuchungen zur vergleichenden Anatomie der Wirbelthiere, 2 Heft. Schultergürtel der Wirbelthiere. Brustflosse der Fische. Leipzig, 1865.
(466) A. Götte. “Beiträge z. vergleich. Morphol. d. Skeletsystems d. Wirbelthiere, Brustbein u. Schultergürtel.” Archiv f. mikr. Anat. Vol. XIV. 1877.
(467) C. K. Hoffmann. “Beiträge z. vergleichenden Anatomie d. Wirbelthiere.” Niederländisches Archiv f. Zool., Vol. V. 1879.
(468) W. K. Parker. “A Monograph on the Structure and Development of the Shoulder-girdle and Sternum in the Vertebrata.” Ray Society, 1868.
(469) H. Rathke. Ueber die Entwicklung der Schildkröten. Braunschweig, 1848.
(470) H. Rathke. Ueber den Bau und die Entwicklung des Brustbeins der Saurier, 1853.
(471) A. Sabatier. Comparaison des ceintures et des membres antérieurs et postérieurs d. la Série d. Vertébrés. Montpellier, 1880.
(472) Georg ’Swirski. Untersuch. üb. d. Entwick. d. Schultergürtels u. d. Skelets d. Brustflosse d. Hechts. Inaug. Diss. Dorpat, 1880.
Pelvic girdle.
Pisces. The pelvic girdle of Fishes is formed of a cartilaginous band, to the outer and posterior side of which the basal element of the pelvic fin is usually articulated. This articulation divides it into a dorsal iliac, and ventral pubic section. The iliac section never articulates with the vertebral column.
In Elasmobranchii the two girdles unite ventrally, but the iliac section is only slightly developed. In Chimæra there is a well developed iliac process, but the pubic parts of the girdle are only united by connective tissue.
In the cartilaginous Ganoids the pelvic girdle is hardly to be separated from the skeleton of the fin. It is not united with its fellow, and is represented by a plate with slightly developed pubic and iliac processes.
In the Dipnoi there is a simple median cartilage, articulated with the limb, but not provided with an iliac process. In bony Ganoids and Teleostei there is on each side a bone meeting its fellow in the ventral line, which is usually held to be the rudiment of the pelvic girdle; while Davidoff attempts to shew that it is the basal element of the fin, and that, except in Polypterus, a true pelvic girdle is absent in these types.
From my own observations I find that the mode of development of the pelvic girdle in Scyllium is very similar to that of the pectoral girdle. There is a bar on each side, continuous on its posterior border with the basal element of the fin ([figs. 345] and [347]). This bar meets and unites with its fellow ventrally before becoming converted into true cartilage, and though the iliac process (il) is never very considerable, yet it is better developed in the embryo than in the adult, and is at first directed nearly horizontally forwards.
Amphibia and Amniota. The primitive cartilaginous pelvic girdle of the higher types exhibits the same division as that of Pisces into a dorsal and a ventral section, which meet to form the articular cavity for the femur, known as the acetabulum. The dorsal section is always single, and is attached by means of rudimentary ribs to the sacral region of the vertebral column, and sometimes to vertebræ of the adjoining lumbar or caudal regions. It always ossifies as the ilium.