PELVIC GIRDLE. 607 



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 generally meet the corresponding elements 

 of the opposite side ventrally, and form a symphysis with them. 

 The symphysis pubis, and symphysis 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 formed as independent masses of cartilage, which 

 subsequently unite in the ventral line. 



In the Urodelous Amphibia (Triton) each mass is a simple 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 

 a single ossification in its posterior part which forms the ischium ; while 

 the anterior part, which may be considered as representing the pubis, 

 usually remains cartilaginous ; though Huxley (No. 475) states that it has 

 a separate centre of ossification in Salamander, which however does not 

 appear to be always present (Bunge). There is a small obturator foramen 

 between the ischium and pubis, which gives passage to the obturator nerve. 

 It is formed by the part of the tissue where the nerve is placed not be- 

 coming converted into cartilage. 



There is a peculiar cartilage in the ventral median line in front of the 

 pubis, which is developed independently of and much later than the true 

 parts of the pelvic girdle. It may be called the praepubic cartilage. 



Reptilia. In Lacertilia the pelvic girdle is formed as a somewhat 

 triradiate mass of cartilage on each side, with a dorsal (iliac) process, and two 

 ventral (pubic and ischiad) processes. The acetabulum is placed on the 

 outer side at the junction of the three processes, each of which may be 



