MORPHOLOGICAL REVISION 105 



"The posterior prolongations or quadrate processes of the pterygoids, arising 

 just back of the transverse bones from the base of the stout sphenoid processes, are 

 long, thin, divergent, oblique plates of bone, extending back nearly to the hind 

 margin of the skull, articulating broadly but loosely with the plate of the quadrate 

 as shown by the dotted lines in figure 3, plate 12 (of this paper). The inner border 

 nearly touches the sides of the basisphenoid; the lower, thin and nearly straight 

 border is continued to near the articular extremity of the quadrate. The basisphe- 

 noid is narrow in front, gradually widened behind, grooved in the middle, shallower 

 in front, more deeply behind, where it is bordered on each side by a descending 

 process which terminates in a free, thin margin underhanging a fossa that opens 

 backward. I can not distinguish with certainty the sutural division between the 

 basisphenoid and basioccipital, though it seems to be wholly back of the lateral pro- 

 cesses, since in another skull, in which the basioccipital has been dislodged, the 

 division has been made back of these processes. On either side of the basisphenoid, 

 or the conjoined basisphenoid and basioccipital, an elongate, cylindrical or oval 

 rod is given off, which is directed downward, outward, and backward, lying closely 

 under the posterior end of the pterygoid plate, and reaching nearly or quite to the 

 head of the quadrate. This process, clearly the stapes, seems to be suturally united 

 with the basisphenoid, as indicated in figure 1, plate 12 (of this paper). The position 

 of the bone in the specimen seems to be quite normal and undistorted, and the bone 

 is nearly complete, though possibly the extreme end has been broken away; it seems 

 to be perforated proximally by a small foramen. The shape, form, and relations of 

 the basisphenoid, stapes, and pterygoids may be compared with the author's figure 

 of the same parts in the remarkable rhachitomous amphibian recently described by 

 myself.* 



"The basioccipital bone, limited as I believe it to be in front, is small and is 

 clearly distinguishable from the exoccipitals. Its condyle is convex, oval from 

 side to side, somewhat pitted in its middle, and seems to be wholly composed of the 

 basioccipital. The exoccipitals are small, apparently taking no part in the condyle. 

 The suture limiting them from the basioccipital is clearly seen at the sides below 

 and joining the margin of the foramen immediately at the side of the condylar surface 

 above. The suture separating it from the paroccipital passes through the jugular 

 foramen, thence directly upward and forward. The exoccipitals join the supra- 

 occipital by a transverse suture a little below the summit of the foramen magnum. 

 The foramen magnum is heart-shaped, about eight millimeters in its greater diameter. 

 The paroccipitals or opisthotics are distinct elements, the distinguishing suture very 

 clearly indicated, as already stated. They are stout at their base, and are turned 

 outward and backward to end in a short cylindrical rod lying under the prox- 

 imal posterior end of the quadrate and articulating at the extremity with the facet 

 already described on the lower part of the inner end of the 'epiotic' This articular 

 arrangement is the normal one of the opisthotic with the epiotic in the Stegocephala. 

 Chiefly because of this fact I am loath to identify the bone with the quadratojugal, 

 to say nothing of the anomalous position of the bone for a quadratojugal. Anteriorly 

 the suture separating the paroccipital from the supraoccipital passes nearly directly 

 forward to the outer side of the posterior lateral projections of the supraoccipitals 

 where the dividing suture turns inward. Of the suture separating the prootics I 

 am less certain, though it seems to be quite apparent in the position I have figured 

 it in the drawing. The supraoccipital is a large element, when seen from above 

 having a marvelous resemblance to the arch of a dorsal vertebra. A small dorsal 



* Trematops milleri, Journal of Geology, vol. xvn, p. 636, 1909. 



