Apr. 1903. North American Plesiosairs — Wii.liston. 



27 



for the pituitary, a narrow roof under the parietal, an open vacuity 

 posteriorly in the supraoccipitals, and with a relatively large otic 

 capsule. The exoccipitah unite obliquely with the basioccipital, tak- 

 ing no part in the formation of the condyle. The paroccipital pro- 

 cesses are small and slender, and there is no indication of a distinct 

 ossification. They are dilated slightly at the extremity, where they 

 abut against the upper part of the quadrate. They are directed down- 

 ward and outward, the distal extremity reaching a level below the 

 top of the occipital condyle. The occipital foramen is transversely 

 Oval, if the upper end is assumed to be near the top of the exocci- 

 pitals, which. show a slight angularity at the place of their union with 

 the separated supraoccipitals. At 

 tin upper posterior extremity of 

 each exoccipital there is a small, 

 deeply excavated, angular cavity, 

 excavated almost wholly from the 

 exoccipital, its upper border only 

 touching the posterior angle of the 

 supraoccipital. Its excavated sur- 

 face is smooth and sharply angu- 

 lar, looking upward and inward. 

 This surface probably corresponds 

 to the smooth tendinous surface 

 seen on the outer angle of the supra- 

 occipital, extending slightly on the 

 corresponding angle of the exocci- 

 pital, in the crocodile. At the 

 posterior part, the exoccipitals 

 approach each other rather closely. 



leaving about four millimeters of basioccipital space in the circumfer- 

 ence of the foramen magnum. Anteriorly, however, the two bones 

 diverge rather widely, terminating a little posterior to the suture 

 separating the basioccipital from the basisphenoid. On the inner 

 side, back of the middle of the bone, and a third of the distance above 

 the sutural margin, is the large oval foramen for the vagus, opening 

 exteriorly below the middle of the moderately expanded paroccipital 

 process. The- smaller foramen for the hypoglossal is situated mid- 

 way between this and the posterior margin, and nearer to the sutural 

 surface ; it opens near the vagal orifice. The sutural surface for the 

 supraoccipital is flat and broadly triangular, pierced near its middle 

 by a small foramen leading into' the posterior semicircular canal in 

 the supraoccipital, the floor of which is seen on this surface, leading 



Dolichorhynchops osborni. Occipital view of 

 skull, x l / } . l\i.. parietal; .»</.. squamosal; 1/.. 

 quadrate: so., supraoccipital; co.. exoccipital; 

 //.. pterygoid; <><'.. occipital condyle; /v.. basl 

 occipital. 



