Shufeldt : OsiKoi.oGV OF THF Hkrodiones. 237 



major portion of the pchis, are more or less pneumatic. The caudal 

 elements do not seem to enjoy this condition. 



There is considerable difference in size in the skeletons of the male 

 and female P/(xat//s, and this difference is very well seen in the pelvis 

 of the two sexes. In the male the /'c/v/s has a length of 6 cm. and an 

 extreme width of 3.7 cm., the first measurement being a medium one, 

 taken between the anterior points of the ilia to the line of articulation 

 between the posterior extremity of the sacrum and the first vertebra of 

 the tail. Measuring the pelvis of a female in the same manner, we find 

 these lines to be respectively 5.2 cm. and 3. i cm. in length and width. 

 Upon the dorsal aspect we find the anterior margins of the ilia to be 

 transverse, with their antero-median angles slightly i)roduced for- 

 wards. These bones here extend somewhat beyond the first vertebra 

 of the sacrum. Their preacetabular |)ortion is concaved and smooth, 

 having the surface upon either side looking forwards and outwards 

 posteriorly, the direction gradually changing as we pass to their 

 anterior ends so as at last it conies to face almost directly upwards. 

 Mesiad, they completely fuse with the superior border of the sacral 

 crista, and in such a manner as to entirely close the neural canals 

 behind. 



Passing to the postacetabular region, it is seen that the mesial 

 margins of the ilia do not fuse with the external borders of the sacrum, 

 while the latter, being of the elongate-lozenge form, has a very reg- 

 ular double row of interapophysial foramina down its length. These 

 foramina begin small anteriorly and gradually increase in size as we 

 proceed towards the tail. The superficial surface of the postacetabular 

 part of an ilium is about half as wide as it is long, being moderately 

 convex anteriorly and concaved behind. 



Posteriorly, both ilium and ischium project considerably beyond the 

 hinder end of the sacrum. On a side view of this pelvis we find the 

 inner ring of the cotyloid cavity to be rather smaller than the outer 

 one ; the antitrochanter is small ; while the ischiac foramen is of good 

 size, and broadly elliptical in outline. Posterior to this latter the 

 side of the bone is much cohcaved, and distally there is a sharp angular 

 notch existing between the ilium and the ischium, similar in character to 

 the one found in Tantalus. The lower ischial margin is sharp, and 

 it is only the extreme poster© -inferior angle of this bone that comes in 

 contact with the upper border of the corresponding pubic style. This 

 leaves between them an open obturator foramen, and an elongated 



