82 



THE OSTEOLOGY AND MYOLOGY 



5. The Posterior Extremity. 



In each half of the pelvic arch and its appendages there are forty-six hones ; they are 

 arranged as follows : — pelvic, four ; femoral, one ; in the knee, two (counting the rudi- 

 mentary patella) ; crural, two ; tarsal, eight ; metatarsal, five ; phalangeal, fourteen ; sesa- 

 moids of the foot, ten. The eighth tarsal is the ossicle supporting the small cartilaginous 

 spur. The patella scarcely deserves to be included in the enumeration ; it consists at best 

 but of specks of ossification ; the other bone of the knee is the fibular fabella, which, 

 though called sesamoid, is distinctly articulated with the fibula. 



Ossa innominata. — (Fig. 24.) Bony union of the ilium, ischium and pubis occurs 

 late, traces of separation being still distinct in adult specimens. The pubis forms less 



of the acetabulum than either of the other two ; the ischium con- 

 tributes the most. (Fig. 24, outline.) The cotyle is ample, both in 

 depth and breadth, having a conspicuously raised, sharp, bony bor- 

 der around about three-fourths of its circumference ; the remaining 

 part of its margin (ischiatic and anterior) is much lower, without a 

 sharp ridge, rising gradually in front to meet the pubic ridge, sep- 

 arated posteriorly from the ischiatic ridge by a narrow but deep 

 groove — the ischiatic ridge terminating abruptly, with almost a 

 process overhanging this groove. In the recent state this de- 

 pressed part of the acetabular rim is made up with ligamentous 

 tissue. In mature individuals there is no distinct articular ossicle, 

 or "epiphysis of the ilium" like that described by Owen as exist- 

 ing in the immature Potoroo (Comp. Anat. Vert., ii, p. 357), nor a 

 second similar ossicle at the ischio-pubic symphysis. The synost- 

 eosis of the three bones at the acetabulum appears uninterrupted. 

 Some irregularity of superficies that is apparent at the ilio-pubic 

 junction may indicate the existence of such ossicle in specimens 

 younger than those examined. The floor of the acetabulum is 

 frequently so thin as to be diaphanous. 

 The contour of the innominate bone may be best gathered from the figure, which is 

 drawn in the plane of the expanded ischium. It is spatulate in general shape, with the 

 long, straight ilium for the handle of the spoon. The ischiatic tuberosity is not produced 

 much backward of the axis of the ilium, nor notably curved in any direction, though a little 

 so outward ; it is obtusely rounded, and little more thickened than the main plate of the 

 bone. The posterior or ''ascending" ramus of the ischium inclines a little obliquely inward 

 toward the acetabulum ; its stout posterior border forming a ridge which mounts behind the 

 acetabular wall to be continuous with the ilium above ; its outer face is rendered concave, by 

 the uprising of the cotyloid brim. The lower border of the ischium offers a gentle, un- 

 broken curve to the pubic symphysis. This border, and the pubic symphysis, are both of 

 great length ; their union is indicated by a slight prominence, above which the symphysis 

 mounts in a nearly straight line. On the pubic ramus, just at the symphysis, lies the 

 smooth, narrowly oval prominence for the articulation of the marsupial bone ; between 

 this and the cotyle the pubis is slenderer than elsewhere. The obturator foramen is 

 large, and sub-circular in shape — its chief irregularity of contour being produced by an 



Fig. 24— Right half of Pelvis. 



