6 OSTEOLOGY OF PTERANODON. 



these buttresses may be termed basipteryc/oids, as they are evidently outgrowths of the 

 basisphenoid. It is impossible to determine to what extent the pterygoids share in the 

 formation of these parts, many of the elements being, as previously stated, so completely 

 fused as to obliterate the original sutures ; but it will be in strict agreement with the 

 usual interpretation of the reptilian skull to consider the outer portions uniting with the 

 inner sides of the quadrates as parts of the true pterygoids. 



From the middle of the anterior edge of each of these pterygoid buttresses, a thin 

 ribbon of bone about 1 cm J n width extends forward and slightly outward, widening a 

 little anteriorly until its outer border becomes confluent with the palatal border or shelf 

 of the maxilla at a point about 5 cm in front of the quadrate. The inner border of 

 this palato-pterygoid ribbon, forming the boundary of the great palatal vacuity or pos- 

 terior nares, can be traced in skull No. 2440 (which is of similar size to the type skull) 

 to about 10 cm in advance of the quadrate. Other fragmentary skulls of the genus 

 show that in this region the inner margins of the palato-pterygoids converged, but no 

 specimen in the collection indicates whether any posteriorly directed style in the midline 

 separated the posterior nares. From the large palatal vacuity forward to the tip of the 

 beak, the palate extends as a continuous tract of bone, showing no demarcation between 

 premaxillae, maxillae, paired vomers, and palatines. In front of the basisphenoid there is 

 a small smooth and curved natural edge of bone, supposed by Professor Marsh to be 

 part of the posterior border of the large and simple oval palatal vacuity including the 

 posterior nares. That the skull of this species bore a most remarkable ossification in 

 the roof of the oral cavity anterior to the basisphenoid, was made evident by the for- 

 tunate identification of a fragment of the palato-pterygoid, which had escaped notice when 

 the type was first described. For want of this piece, Professor Marsh was compelled to 

 restore by conjecture the middle third of the palato-pterygoid, and was led to overlook 

 a small but important ossification clearly representing the transpalatine or ectopterygoid 

 of other Reptilia. In Plate V, figures 7 and 8 of the type show the completed palato- 

 pterygoid ribbon with its associated bones, from the under side (figure 7), and the same 

 parts as they would appear from above if the roof of the skull were removed (figure 8). 

 From these figures it is clear that the pterygo-jugal vacuity is bridged across by a small 

 transpalatine whose outer end in the type remains as a conical stub on the inner surface 

 of the posterior end of the maxilla. Not only is the inner end of the transpalatine bone 

 fused with the palato-pterygoid ribbon after the usual manner, but it is continued as an 

 oblique rod backward and inward across the upper surface of the palato-pterygoid, its 

 broken inner extremity actually projecting freely into the posterior part of the large 

 palatal vacuity. Plate V, figure 9, shows the same portions of the palato-pterygoid and 

 transpalatine in skull No. 2440, as seen from above. The precise form of this extraor- 

 dinary oblique rod at its origin near the midline of the skull is not shown in any speci- 

 men of P. longiceps, but comparison with the almost identical structure seen in the type 

 of P. ingens, No. 2594 (Plate IV, figure 2), demonstrates beyond all possibility of doubt 

 that these remarkable ossifications are lateral outgrowths from the base of the para- 

 sphenoid. 



It is difficult to compute the true form of the upper margin or ridge of the skull. 

 Specimens crushed laterally at first sight seem to indicate a form quite different from 

 those crushed vertically. Professor Marsh, whose material was mainly of the former 

 description, stated : " A sharp ridge extends from the end of the premaxillaries along 

 the median line to the true cranium, and is continued backward by the thin elevated 



