MORPHOLOGICAL REVISION 121 



cavity as a whole had a high arched roof, with a slender, almost vestigial, 

 parasphenoid dividing the large pterygoidal vacuities so characteristic of 

 the amphibia. The internal nares are larger than the external ones, situated 

 either close to the teeth, with their front margin almost below the hind 

 margin of the external nares. On the inner side of each there is a stout, 

 conical, recurved tooth, about lo or 12 millimeters in length, and another 

 like it is situated near the posterior margin of the orifice, not far from the 

 maxillary teeth. These are the only teeth located on the palatal surface. 

 The palatines or conjoined palatines and pterygoids on each side posteriorly 

 and internally to the nares slope strongly upward. In the middle in front 

 the vomer or anterior end of the parasphenoid is about 15 millimeters in 

 width where it joins the palatine shelf, narrowing to about 4 where it joins 

 the rhinencephalic chamber. Posteriorly the arrangement of the basi- 

 cranial bones is very similar to that of Trematops or Eryops. The ossified 

 basisphenoid sends downward and outward a stout basipterygoid process to 

 join the pterygoids on each side, the juncture indicated by a thickening as in 

 Trematops. Outwardly the pterygoids form a vertical plate, probably with 

 the conjoined epipterygoids, reaching to the cranial wall, save for a small 

 vacuity near the roof, leading into the deep temporal cavity under the roof, 

 into which the post-temporal vacuity also opens, a cavity open below back 

 of the pterygoids between the basicranial bones and the posterior wings of 

 the pterygoids. In the middle the parasphenoid continues forward from 

 the basisphenoid as a slender rodlike bone nearly to the flat anterior end. 

 For a short distance it forms a high bridge, above which in front is the infe- 

 rior opening of the parietal foramen. For the larger part of its distance, 

 however, it is closely united as a thick ridge to the lower side of the elongated 

 rhinencephalic chamber. Between this chamber and the closed brain-chamber 

 behind there is a large orifice on each side for the escape of the optic 

 nerves. This elongated arched chamber has its anterior borders also free 

 and curved a little back of the anterior margin of the orbits. In front of 

 this the roof of the skull has been somewhat pressed down upon the palatal 

 bones, but there was evidently in life a high cavity for the nasal region, in 

 which are various indeterminate bone remains, doubtless the ethmoidal 

 and turbinate. A little in front of the basisphenoid the pterygoids give off 

 a rounded or subangular process, much as in the allied forms, narrowing the 

 opening of the infratemporal fossa, which is broad and deep behind, where 

 its thin upper posterior roof forms the anterior inferior wall of the otic 

 cavity. 



"The basisphenoid is concave in the middle; on either side it has a 

 flattened basisphenoid process, as in Trematops, directed downward and 

 backward, underarching a rather deep fossa. Opposite these on either side 

 is the root or base of the pointed, stylelike stapes, which is directed outward 

 and backward to terminate, as already described, at the upper angle of the 

 quadrate, in the auditory vacuities. Whether or not it has a foramen at its 

 base I can not say. Above and in front of this, turned upward to reach nearly 

 to the inner surface of the superior tympanic ridge, is the prootic bone. 



"A comparison of the structure of the basicranial region with that of 

 Trematops shows great similarity, quite confirming my suggestion that the 

 pseudotemporal vacuity is in reality merely the closed otic notch for the 

 opening of the external ear. The opening in Trematops, however, is far 

 smaller than in Cacops, and extends somewhat further forward toward the 



