90 BULLETIN UNITED STATES GEOLOGICAL SURA^EY. [rc^Vl. 



larly wortby of notice on account of their marked individuality, all of 

 them being distinct and nearly circular. The tympanies are free bones, 

 and carry out all the usual functions assigned to them. The mastoid 

 condyle is long, affording by its extension an additional margin at the 

 under side at the end of the bone for attachment of the ear-drum ; the 

 neck between it and the orbital process is somewhat constricted, and 

 presents a large pneumatic foramen on the inner surface. The pointed 

 orbital processes extend upwards, forwards, and inwards, slightly clubbed 

 at their extremities ; they project into the space half-way between the 

 pterygoid and wing-like post-frontal. The mandibular condyle is double ; 

 the inner one is a semi-ellipsoid, placed transversely ; the outer an irreg- 

 ular figure, and separated from the inner by a shallow pit. The oval, 

 cup-shaped cavity for the reception of the tympanic extremity of the 

 squamosal looks directly forward. Between the orbital process and inner 

 mandibular condyle, on the free edge of the bone, is seen a small artic- 

 ular surface for the tympanic extremity of the pterygoid. The pterygoids 

 diverge from each other towards the tympanies by a very open obtuse 

 angle. They are slender and scale-like, being compressed from above 

 downwards, twisted on themselves at their tympanic extremities, caus- 

 ing the long axis of the articular facets for the articulation with these 

 bones to be vertical. As already described, they have a m.id-posterior 

 facet, which meets the pterapophysial process of the basi-sphenoid. An- 

 teriorly they do not touch each other, but articulate with the extremities 

 of the palatines, and the combined four bones touch, and in the living- 

 bird glide over for a limited distance the lower border of the rostrum of 

 the basi-presphenoid. The anterior ends of the palatines articulate by 

 an anchylosed schindylesial articulation between the lower surfaces of 

 the maxillaries and the thin upper surface of a bony process extending 

 backwards from the intermaxillary. From this point they slightly di- 

 verge from each other and become broader, being broadest about their 

 middles 5 they then rather abruptly approach each other posteriorly, where 

 they form the joint with the pterygoids already described. Their pos- 

 terior ends are kept slightly apart by the lower border of the presphe- 

 noid. They are flattened from above downwards throughout their en- 

 tire extent. Their outer borders are sharp, and form from one end to 

 the other a long convexity. As the inner and concave borders ap- 

 proach eacli other posteriorly they develop a raised rim on their under 

 sides, thereby affording a greater surface lor muscular attachment. 

 Above, near their middles, they aid the maxillaries (and in large part de- 

 veloped from them) in supporting on either side an irregular spongy bone, 

 that serves the double purpose of narrowing the apertures of the poste 

 rior nares and adding bony surface to the roof of the mouth by constric- 

 tion of the palatine fissure. As is the rule in nearly all birds, the tym- 

 panic end of the infraorbital bar is on a lower k^vel than the maxillary 

 extremity ; it is received into tlie cup-like articulating cavity on that 

 bone. The two oblique sutures, persistent in many birds, and denoting 



