230 ME. W. P. PYCEAFT ON THE MOEPHOLOGY AND 



is convex, and forms, with its fellow of the opposite side, a long tunnel divided into 

 right and left halves by the neural spines of the synsacrum, which acts as a median 



partition. 



The dorsal plane, which in JDrommis, Casiiarivs, and Bhea was restricted to a small 

 area between the supra-trochanteric processes, here, in StnitJiio, extends backwards to 

 the extreme end of the post-acetabular ilium, though it is very narrow. Furthermore, 

 this plane slopes gently downwards on either side, so that its extremest outer angles 

 approach the anti-trochanter. 



The pre-acetabular ilium meets in the mid-dorsal line above the synsacral spines : the 

 post-ace tabular ilia remain widely separated one from another throughout the greater 

 part of tlieir length ; in old individuals they meet and fuse with the last two post- 

 sacral vertebras of the synsacrum. Down the median space, between the two post- 

 ilia, runs a long bony bar, formed by the fusion of anterior and posterior ossifications 

 of the neural spines. In DinornifhkJa>, it will be remembered, it was pointed out [i] 

 the equivalent ossifications extended laterally, so as to reach the ilia on either side, and 

 thus close what would otherwise form a deep lateral trench lying on either side of the 

 synsacrum. Tliis trench in Strutliio remains permanently open. 



The iscMinn is very slender and rod-shaped. At its posterior extremity it sends 

 downwards a broad plate of bone which fuses with the pubis. In the young bird, it 

 should be mentioned, the ischium is free posteriorly. The post-acetabular ilium and 

 the ischium remain widely separated throughout life. 



The jmhis is long, slender, and rod-shaped. In the adult it extends caudad far 

 beyond the post-ilium and ischium, and curving sharply downwards and forwards, meets 

 its fellow of the opposite side in the middle line, and becomes permanently fused 

 therewith in a long, forwardly directed symphysis. This fusion of the pubes posteriorly 

 occurs in no other living bird. 



As is well known now, the pubis of StrutMo is further remarkable for a small bony 

 plate, attached to the middle of its ventral border by cartilage. In macerated 

 skeletons this is generally lost ; in this case its position is indicated by a roughened 

 surface. 



This bone appears to have been originally described by Meckel [56], who held it to 

 represent the marsupial bone of the Marsupials. More than forty years later this bone 

 was rediscovered and described by Garrod and Frank Darwin [28]. They also regarded 

 it as probably homologous with the marsupial bone of the Kangaroo and its allies. 

 With this view Beddard [7] seems also to agree. 



The pectineal process is long, slender, and curved, its free end being directed 

 upwards. 



The ilio-ischiadic fissure remains permanently open in Struthio. In Casiiarius and 

 lJrom(eus and in Rhea it closes later in life. The obturator fissure is closed, by fusion 



