PROFESSOR OWEN ON THE GENUS DINORNIS. 245 



augments to 1 inch 2 lines in the eleventh (ib. ii) ; thence this dimension gradually 

 decreases to the breadth of 7 lines in the seventeenth sacral (ib. 17), slightly increasing 

 in the eighteenth (ib. is), which presents the characters of a coalesced caudal vertebra. 

 The neural spines of the sacrals are confluent throughout ; that of the first, 2 inches 

 2 lines in length, has part of its summit (PI. LIII. fig. 2, s 1) e.xposed at the angle of 

 divergence of the ilia (ib. 62) ; the following ten spines have coalesced with each other 

 and with the upper or neural margins of these bones ; the succeeding similarly coalesced 

 sacral spines do not reappear until the divergence of the ilia (ib. C2«) at the eleventh 

 sacral vertebra. The summits of the neural spines thence to the fifteenth vertebra 

 are exposed to form a flat horizontal plate (ib. n, s), the side borders of which coalesce 

 with mesial ones of the diverging ilia; this coalescence ceases at the spine of the 

 fifteenth sacral, whence the coalesced flattened summits of the rest converge to the 

 eighteenth, terminal vertebra (ib. is). The thick pleurapophyses (ib. pi) of the last 

 three sacrals are exposed at the interspaces between their spines and the iliac bones. 



The outer surface of the anterior two thirds of the ilium (ib. fig. 1, 62) is smooth, 

 moderately concave, marked by a few vascular grooves ; it forms the upper three 

 fourths of the acetabulum (ib. a), and the surface (b) for the femoral trochanter con- 

 tinued therefrom backward and upward ; this surface is feebly concave vertically, convex 

 lengthwise. The outer surface of the ilia behind their divergence is bent downward 

 at a right angle with the horizontal flattened part ; the extent of the downbent part 

 ( 02' ) is 4 inches, its vertical diameter is 1 inch ; but this part of the bone is triedral, 

 the third and inner surface inclining downward and inward to receive the coalesced 

 ends of the abutting processes of the fourteenth to eighteenth vertebra; inclusive. 

 The admeasurements of the pelvis give the chief ones of the iliac bones. 



The ischium (03), after contributing part of the lower and hinder wall of the aceta- 

 bulum, contracts to a subcylindrical bar of 6 |lines diameter and of like length ; it 

 then expands with the lower border almost in contact with the pubis (64), the opposed 

 rough surfaces indicating a fibrous union there 6 lines in extent, defining the hole (q) 

 for the passage of the tendon of the ' obturator internus ' muscle. Beyond this the 

 ischium loses thickness and gains in breadth, attaining that of 2 inches at its free 

 hinder end ( 63' ) ; this is 1 inch distant from the ilium above, and ^ an inch from the 

 free end of the pubis below. The ischia bend slightly inward towards their expanded 

 ends, which are 3J inches apart at the upper angle, and 5 inches at the lower angle of 

 the bone. 



The pubis (64), contributing the lower and fore part of the acetabular wall, contracts 

 to a thickness of 5 lines, and assumes beyond the obturator foramen (q) a subtriedral 

 figure, flattened on the outer facet, and slightly expanding at its terminal upcurved 

 extent of one inch and a half to a depth or breadth of 8 lines ( 64' ), with an interspace 

 between it and the ischium of 5 lines. 



The cavity of the acetabulum (a) presents the usual circular form, with a diameter 



