136 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [Yol.YI. 



this remarkable compound bone, and the aid of a strong light, that they 

 can with any satisfaction be counted. There are eleven of them ; excep- 

 tionally, twelve. 



The neural canal, circular at the outstart, shows the ns.ual pelvic sicell, 

 chiefly anterior to the acetabula, conformable with the ventricular dila- 

 tation of the myelon in that locality. The exit of this tube distally is 

 likewise nearly circular. The foramina along the bodies of the centra, 

 in the vicinity of the dilatation referred to, are double and placed one 

 above another, for the separate egress of the roots of the pelvic plexus- 



The anterior aspect of the first sacral vertebra presents every element 

 and process requisite for articulation with the ultimate dorsal segment. 

 It is largely overshadowed by the ossa innominata. Opposite the iliac 

 contraction, in the neighborhood of the fourth and fifth sacrals, these 

 vertebrae throw out their par- and di-apophysial processes far enough to 

 meet and brace the ihac bones. We do not meet with such braces again 

 until arriving opposite the acetabula and beyond, where the parapo- 

 physes project upwards and unite with the outer margins of the trans- 

 verse processes, the ilia articulating with the free and united borders. 



Foraminal deficiencies not unusually occur among these processes, more 

 particularly between the last two sacrals, where they seem to be con- 

 stant, though of varying size and shape in different individuals. 



The last sacral vertebra is markedly compressed from above down- 

 wards, retaining, however, all the elements required in articulation with 

 the first and much-modified coccygeal vertebra. 



Viewing the confluent sacral vertebrae, or the " sacrum^\ from above, 

 we find the united neural spines, as a vertical lamina, dividing the ante- 

 rior interiliac space into two capacious ilio-neural grooves at that moiety 

 of the bone. 



This common neural spine and the ilio-neural grooves proceed back- 

 wards uutil the gluteal ridge of the ilium curves outward to the antitro- 

 chanter on either side. At this point the spine disappears with the 

 grooves, the sacrum becomes nearly flat and spreads out, to gradually 

 contract again before its ultimate dilatation in the diapophyses of the 

 last vertebra. 



The ornithotomist will find, in reviewing the skeletons of our avian 

 types that the ilio-neural grooves, as seen in this bird, are very fre- 

 quently converted into canals in other orders, by meeting of the inter- 

 ested bones above. The condition as defined, however, in the previous 

 paragraph, as relating to Eremophila, seems to be characteristic of Amer- 

 ican Oscines. The sacrum is slightly convex from before backwards on 

 its upj)er surface, moderately concave along the confluent centra below. 



The pelvis of this bird is uncommonly wide and short, and the ischi- 

 adic and pubic posterior extremities remarkably flared outwards. The 

 anterior and inner angle of each ilium, apparently assisted by the dia- 

 pophysis of the first sacral vertebra from beneath, is pointed ; the ante- 

 rior border slopes backwards gradually, for a distance of 3 or 4 rnUli- 



