498 PELVIC GIRDLE. 



section is only sliglitly developed. In Chimaera there is a well deve- 

 loped 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 con- 

 verted 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 vertebrae 

 of the adjoining lumbar or caudal regions. It always ossifies as the 

 ilium. 



The ventral section is usually formed of two more or less separated 

 parts, an anterior which ossifies as the pubis, and a posterior which 

 ossifies as the ischium. The space between them is known as the 

 obturator foramen. In the Amphibia the two parts are not separated, 

 and resemble in this respect the pelvic girdle of Fishes. They gene- 

 rally meet the corresponding elements of the opposite side ventrally, 

 and form a symphysis with them. The symphysis pubis, and sym- 

 physis ischii may be continuous (Mammalia, Amphibia). 



The observations on the development of the pelvic girdle in the 

 Amphibia and Amniota are nearly as scanty as on those of Fishes. 



Amphibia. In the Amphibia (Bunge, No. 473) the two halves of 

 the pelvic girdle are fortned as independent masses of cartilage, which 

 subsequently unite in the ventral line. 



In the Urodelous Amphibia (Triton) each mass is a simjile plate of 

 cartilage divided into a dorsal and ventral section by the acetabulum. 

 The ventral parts, which are not divided into two regions, unite in a 

 symphysis comparatively late. 



The dorsal section ossifies as the ilium. The ventral usually contains 



