2Vo. 4] SHUFELDT ON THE OSTEOLOGY OF SPEOTYTO. 105 



each other, and form the gluteal ridges and borders of those scale-like pro- 

 jections of the posterior portion of the ilia that overhang the acetabula. 

 Produced now as the "gluteal ridges", they tend almost directly back- 

 wards, though very slightly inwards, to terminate in the ischial mar- 

 gins. The preacetabula dorsal iliac surfaces are generally concave, 

 while the postacetabula, and at the same time that surface which 

 occupies the higher plane, is flat, having a slope downwards and 

 backwards, with a ventral reduijlication after forming the rounded and 

 concave posterior boundary of the pelvis. The preacetabula super- 

 ficial iliac area is nearly double the extent of the postacetabula. 

 The antitrochanterian facets that surmount the cotyloid ca\ities have 

 the usual backward direction, though their surfaces look downwards, 

 outwards, and a little forwards. The external surfaces of the iscMa look 

 upwards and outwards, having just the reverse direction ventrally. 

 Posteriorly, these bones are produced beyond the ilia into finely pointed 

 extremities, tending to approach each other. The slender pubic bones, 

 after closing in the obdurator foramen on either side, touch and unite 

 with the inferior borders of the ischia as far as the pointed ends of the 

 latter, beyond which they are produced nearly to meet behind. The in- 

 terval between the free extremities of the pubic bones in some individ- 

 uals, notably ''birds of the year ", is very slight, less than a millimetre 

 sometimes, approaching a closed pelvis. The circular and thoroughly 

 perforated acetabula are formed in the usual manner by the three pelvic 

 bones. They have a diameter of about three millimetres, and their cir- 

 cumferences are in the vertical plane. The ischiadic foramina are ellip- 

 tical and large ; they are, as usual, posterior to the acetabula and above 

 the obdurator foramina. These last are also elliptical, and about one- 

 third the size of the others. Should the major axes of these two ellipses 

 be produced backwards, they would intersect and form an acute angle 

 just within the posterior pelvic border. Viewing the pelvis ventral- 

 wise, we observe, in addition to points mentioned when speaking of the 

 sacrum, the reduf)lication of the ilia, forming pockets behind and inter- 

 nally, that open outwards through the ischiadic foramina and inwards 

 into the general pelvic cavity. The pelvic passage is subcircular, un- 

 closed, with an average diameter of 1.7 centimetres vertically, and a 

 little less transversely. The narrowest part of the pelvis measures 1.3 

 centimetres, the widest 2 centimetres, being taken between the iliac pro- 

 jections over the acetabula ; the average length, including anterior neural 

 spine, is 3 centimetres. Pneumatic foramina occur in the shallow an- 

 fractuosities, between the antitrochanters and gluteal ridges in the ilia. 

 iNone of the caudal vertehrcc are grasped by the pelvis, the posterior ex- 

 tremity of the sacrum always assisting to form the curve of the i^elvic 

 passage. The usual number of these vertebne is seven, though occa- 

 sionally an additional one is found, making eight in some individuals. 

 This enumeration does not include the modified and ultinmte coccygeal 

 vertebra, the pygostyle. They are all freely movable upon one another, 



