ON THE SKULL OF NYCTODACTYLUS 523 



sinus in front of the prefronto-lachrymal bone. The bone evi- 

 dently continues over the outer surface of the maxillary process 

 to unite with the lachrymal, and perhaps also with the ascending 

 process of the malar. On the under side of the premaxillary 

 the bones of the two sides may meet in the middle, though this 

 seems doubtful. 



The prefrontal and lachrymal cannot be distinguished from 

 each other, and there seems to be some disagreement among 

 writers as to which of the two elements should be called the pre- 

 frontal, were they distinguishable. The prefrontal must be that 

 portion articulating along the sides of the premaxillary and 

 frontal, while the lachrymal is that part which forms the anterior 

 or anterior superior border of the orbit, either articulating 

 directly with the frontal and the prefrontal, or with the prefrontal 

 only, which one should expect. In the present specimen the 

 compound element is sharply distinguishable from the frontal 

 and premaxillary, as also the nasal. It begins on the side of the 

 premaxilla a little back of the visible surface of the nasal, to 

 which it is attached, as a slender pointed anterior process, and 

 widens out posteriorly, forming a concave border, to which the 

 thin, imperfectly ossified posterior part of the nasal attaches. 

 Externally it widens out again into the broader horizontal plate 

 forming the anterior superior roof of the orbit, which anteriorly 

 curves downward to meet the jugal. Its orbital margin is thin. 



The jugal bone extends forward on the outer and inferior 

 side of the maxilla to beyond the middle of the nares. How 

 far front it goes cannot be determined. In Ornitho stoma the dis- 

 tinguishing suture, placed as in Nyctodactylus, seems to be con- 

 tinued as far forward as the anterior end of the nares, which 

 would seem to indicate that the premaxilla does not reach as far 

 back as in Rhamphorhynchus. At the front extremity of the 

 orbit it sends up a slender process of bone, superimposed upon 

 a thin expansion of the maxilla, to meet the lachrymal and nasal. 

 Beyond this it forms a narrow bar, four or five millimeters in 

 width, to the lower extremity of the quadrate, and then turns 

 upward and backward a little more broadly to join, by a long 



