SHUFELDT : OSTEOLOGY OF THE STEGANOPODES 159 



This elevation of the center and margins causes the formation of longitudinal de- 

 pressions between them, and down the center of either one of these we find the row 

 of interapophysial foramina, to which reference has already been made above. 



Some Cormorants seem to have a fairly well marked propubic spine, and there is 

 an indication of the rudiment of such a process in the Anhinga. The internal cir- 

 cumference of either cotyloid ring is smaller than the external, and these cavities 

 are brought up very close to the sacrum. Of enormous dimensions is the ischiadic 

 foramen ; it has the effect of absorbing nearly all the ilium above, and to some ex- 

 tent behind it; while below, it makes the neck of the ischium very narrow indeed. 

 Inform this large foramen is subelliptical. The "obturator foramen" opens into 

 the obturator space, which latter is also extensive, and the pubic style which bounds 

 it below as far as the point where it meets the ischium, is very slender and frail. 

 Beyond this, the pubic bone is in close contact with the lower margin of the 

 ischium, where it is very considerably stouter, as it. also is after it becomes suddenly 

 deflected behind after passing the extreme distal angle of the ischium precisely as 

 as it does in typical Cormorants. 



A deep, triangular ilio-ischiadic notch, between the here very narrow ilium and 

 the far broader ischium, indents the posterior pelvic border. 



The 'antitrochanters are prominent, and the facet on either one of them looks 

 forwards, downwards and slightly outwards. 



Ventrally, the "pelvic basin" is seen to be fairly capacious; the "sacrum" is con- 

 siderably enlarged opposite the acetabulse and beyond ; the exits for the nerves of 

 the sacral plexus are double ; finally, in front, we see the horizontally spreading 

 ilia, with the compressed vertebrae, dipping down anteriorly so far ventrad. 



There are six free caudal vertebrae in the skeleton of the tail of this Darter, 

 plus a large pygostyle. This latter bone is drawn out supero-posteriorly, and the 

 long superior edge is very sharp. Its antero-inferior angle is enlarged, with flattened 

 surface below. Beyond this, the inferior border gradually contracts and becomes 

 rounded. In front there is an extensive pit for articulation with the last caudal 

 vertebra, and above this there is a small opening where the spinal cord enters 

 this bone. 



The centra and their articulatory facets are large in these vertebrae, but the 

 spinal canal is of no great caliber. In mid-series the neural arch and spine, and 

 the forward-projecting prezygapophyscs are conspicuous. A good-sized haemal spine 

 also characterizes the last four vertebra, and in each case it extends forwards to 

 underlap the bone next in advance. As a rule the transverse processes are rather 

 short and stumpy, being entirely rudimentary in the sixth caudal. 



