296 • THE PELVIC GIRDLE. [chap. xvn. 



symphysis is long and generally ossified. In the Kangaroos 

 the pectineal tubercle (//) of the pubis is strongly developed. / 



Nearly all Marsupials have a pair of elongated, flattened, 

 slightly curved bones (Fig. 108, m), moveably articulated 

 by one extremity to the anterior edge of the pubis, near the 

 symphysis, and, passing forwards, diverging from each other, 

 within the layers of the abdominal parietes. They are, in 

 fact, ossifications in, or intimately connected with, the inner 

 tendon or " pillar " of the external oblique muscle, and there- 

 fore come under the category of sesamoid bones. They 

 vary in size and shape in different species. In Didelphys 

 they are nearly as long as the ilia, while in the Kangaroo 

 they are scarcely half the length of that bone. Though 

 largely developed in the Dasyures, in the allied genus Thy- 

 larinus, they are represented only by small, unossified fibro- 

 cartilages. 



These bones are commonly called " marsupial bones," 

 though they have no special function relating to the ventral 

 pouch of the female, being nearly equally developed in both 

 sexes, and also in those species in which the marsupium is 

 not present. 



In ' the Monotremata the pelvis is short and broad 

 The ilia are short, distinctly trihedral and everted above. 

 The ischia are large, and prolonged into a considerable 

 backward-directed tuberosity. The symphysis is long, and 

 formed about equally by pubes and ischium. The thyroid 

 foramen is round. The acetabulum is perforated as in Birds. 

 The pectineal tubercle is greatly developed. There are large 

 " marsupial " bones in both genera. 



