SHUFELDT : OSTEOLOGY OF THE STEGANOPODES 137 



show the same character of venated surface as I described for the superior mandible. 

 Posterior to this, however, as well as the inner ramal aspect, the bone is smooth, 

 having the same appearance as in most birds. 



The symphysis is short and develops a spine behind, which points directly back- 

 ward and is in every respect similar to the process in the same place, between the 

 sides of the lower jaw, in Herons and Albatrosses. Each ramus of this mandible 

 is very thick from side to side, bui these parts are hollow, and the bone as a whole, 

 is very light, owing to the high state of pneumaticity it enjoys. 



The principal foramina for the entrance of air to its interior are four in number, 

 two on either limb, one being to the mesial side of the articular cup, and another 

 larger, longitudinally placed, elliptical one just beyond this concavity on the inner 

 aspect of the ramus near its upper border. The superior side of an articular end 

 has a deep excavation at its center upon which the facets for the quadrate do not 

 encroach, so that, when the jaw is articulated, this pit comes opposite the notch 

 between the trochle£e of the mandibular foot of the quadrate, creating an irregular 

 hollow space there between the bones of no inconsiderable size. When the quad- 

 rate thus covers it there are two entrances that are left open, one in front and one 

 behind, close to the pneumatic foramen. 



The mandibular angles are truncate, very nearly perpendicularly so, their sur- 

 faces being concave and very broadly luniform in outline (Plate XXII., Fig. 7). 



Commencing just in front of an articular cup, we find the superior border of 

 the ramus to be rather wide and rounded as far as the meeting with the dentary 

 This portion presents near its middle a double coronoid process, one being in front 

 of the other. The dentary portion of their border has an outer cultrate edge and 

 an inner and somewhat lower rounded one. 



The outer edge goes to the anterior apex of the symphysis, the inner one to the 

 hinder termination of the same, while between the two a nearly horizontal surface 

 is contained, which gradually becomes narrower as we proceed in the forward 

 direction. 



The lower borders of the mandible are rounded for their entire extent, being 

 produced beneath the articular cups and continuous with the inner boundary of 

 either truncate angular extremity. 



We find that the usual bones which surround the true ramal vacuity on the 

 side of the mandible in many birds, here interlock with each other so as to com- 

 pletely fill the fenestra in, but in rather an unusual way, and apparently, for a 

 definite purpose; for each ramus presents, both on its inner and outer side, an 

 oblique slit, these slits being opposite each other and with their anterior ends in 



