Bibliography.
(473) A. Bunge. Untersuch. z. Entwick. d. Beckengürtels d. Amphibien, Reptilien u. Vögel. Inaug. Diss. Dorpat, 1880.
(474) C. Gegenbaur. “Ueber d. Ausschluss des Schambeins von d. Pfanne d. Hüftgelenkes.” Morph. Jahrbuch, Vol. II. 1876.
(475) Th. H. Huxley. “The characters of the Pelvis in Mammalia, etc.” Proc. of Roy. Soc., Vol. XXVIII. 1879.
(476) A. Sabatier. Comparaison des ceintures et des membres antérieurs et postérieurs dans la Série d. Vertébrés. Montpellier, 1880.
Comparison of Pectoral and Pelvic girdles.
Throughout the Vertebrata a more or less complete serial homology may be observed between the pectoral and pelvic girdles.
In the cartilaginous Fishes each girdle consists of a continuous band, a dorsal and ventral part being indicated by the articulation of the fin; the former being relatively undeveloped in the pelvic girdle, while in the pectoral it may articulate with the vertebral column. In the case of the pectoral girdle secondary membrane bones become added to the primitive cartilage in most Fishes, which are not developed in the case of the pelvic girdle.
In the Amphibia and Amniota the ventral section of each girdle becomes divided into an anterior and a posterior part, the former constituting the præcoracoid and pubis, and the latter the coracoid and ischium; these parts are however very imperfectly differentiated in the pelvic girdle of the Urodela. The ventral portions of the pelvic girdle usually unite below in a symphysis. They also meet each other ventrally in the case of the pectoral girdle in Amphibia, but in most other types are separated by the sternum, which has no homologue in the pelvic region, unless the præpubic cartilage is to be regarded as such. The dorsal or scapular section of the pectoral girdle remains free; but that of the pelvic girdle acquires a firm articulation with the vertebral column.
If the clavicle of the higher types is derived from the membrane bones of the pectoral girdle of Fishes, it has no homologue in the pelvic girdle; but if, as Götte and Hoffmann suppose, it is a part of the primitive cartilaginous girdle, the ordinary view as to the serial homologies of the ventral sections of the two girdles in the higher types will need to be reconsidered.
Limbs.
It will be convenient to describe in this place not only the development of the skeleton of the limbs but also that of the limbs themselves. The limbs of Fishes are moreover so different from those of the Amphibia and Amniota that the development of the two types of limb may advantageously be treated separately.
In Fishes the first rudiments of the limbs appear as slight longitudinal ridge-like thickenings of the epiblast, which closely resemble the first rudiments of the unpaired fins.