86 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



The supraoccipital plates are extended in the same manner. They are 

 separate and form the posterior edge of the skull. In three specimens the 

 parietal of the left side has a greater extension to the rear than that of the 

 right. 



The maxillaries are short, not extending posterior to the orbits. They 

 form the posterior edge of the nares and carry a single row of teeth. 



The jugals are rather broad in front, forming the outer rim of the orbit, 

 articulating with the postorbital-postfrontal and squamosal above and with 

 the quadratojugal and prosquamosal behind. They are elongated in cor- 

 relation with the developing horn. 



The squamosals are smaller than the parietals, prosquamosals, and jugals, 

 between which they lie; they are somewhat elongated, with the horns, but 

 not so much so as the other bones. 



The prosquamosals are large bones forming the bulk of the outer part 

 of the horn. The posterior half of the outer edge is free and forms the edge 

 of the skull; the anterior half is covered by the quadratojugal. On the other 

 sides, the bone articulates with jugal, squamosal, parietal, and tabulare. 



The tabulare forms the apex and a good portion of the horn; its anterior 

 edge is wedged in between the parietal and prosquamosal, touching the 

 extremity of the parietal. 



The quadratojugal lies below the jugal and prosquamosal, and in the 

 normal condition was directed somewhat downward, forming the edge of the 

 fossa, into which fitted the coronoid process of the lower jaw. It supports 

 the quadrate below and with the prosquamosal forms the postquadrate pro- 

 jection on the lower surface of the skull. 



The quadrate is attached to the quadratojugals by the proximal end 

 only; it passes upward and backward and is attached to the under side of 

 the posterior part of the prosquamosal. On the lower surface the general 

 position and relations of the bones are easily made out, but the exact course 

 of the sutures can not be followed in any specimen. 



The premaxillaries and maxillaries form the edges of the very short 

 mouth, and each bears a single row of small, sharp, conical teeth. These 

 have a slightly oval base in some cases, with a large pulp cavity, but without 

 any approach to a labyrinthine arrangement of the dentine. 



The prevomers form a small plate at the anterior end of the parasphen- 

 oid; they form the inner borders of the choanse and bear a small row of sharp 

 teeth, following in general the curve of the premaxillaries. 



The palatines lie on the inner side of the maxillaries and form the inner 

 border of the large palatine vacuities. They are separated by a distinct 

 suture, in some specimens, from the ectopterygoid. A single row of fine 

 teeth follows the curve of the maxillaries, but is separated from the maxil- 

 lary teeth by a considerable space. 



The parasphenoid is wedged in posteriorly between the pterygoids and 

 the exoccipitals; the posterior end terminates in a sharp point which reaches 

 nearly to the edge of the foramen magnum between the two occipital con- 

 dyles. Anteriorly the bone narrows into a long bridge separating the two 

 palatal vacuities, and probably terminates in a sharp point, but the sutural 

 connection with the vomers and palatines can not be made out. 



The exoccipitals support the occipital condyles. They may be con- 

 sidered as formed of two parts, an inner carrying the condyle and forming 

 the border of the foramen magnum and an outer elongated process, probably 



