1888.] PROCEEDINGS OF UNIT2D STATES NATIONAL MUSEUM. 237 



of the fairly well-pronounced supraoccipital elevation. The plane of 

 the occipital area is nearly or quite perpendicular to the plane of the 

 basis era nit. 



Anatidce have their skulls more or less perfectly permeated by air, 

 and when properly prepared are really structures of great beauty, as is 

 the glistening white skull of the Swan before me, which is so exceed- 

 ingly light for its size and withal so graceful in outline. 



Few and unimportant are the differences that are found to exist be- 

 tween any two mandibles of representative Anatidce, the general type of 

 the structure being quite a uniform pattern, as it prevails throughout 

 the entire group. Perhaps Spatula offers us as great a departure from 

 the common form of the anatidine mandible as any American Duck we 

 have, and even here we find, on side view, that it possesses all the essen- 

 tial characters, of the bone as found in the group. Seen upon this latter 

 aspect we have presented us for examination the lamelliform and ver- 

 tical angular processes. These are greatly produced directly backward, 

 to be abruptly recurved upward at their extremities. 

 This is the style also in Olor, but in Hutchiu's Goose 

 they are saber shaped and gradually recurve upward. 

 Beyond this process the articular facet projects from 

 the ramal side, and at a varying distance (for the 

 species) in front of this we find a constant process for 

 muscular attachment. This last is situate at about 

 the middle of the deepest and most plate-like portion 

 of the ramus, and in a Swan is ridge-like, being con- 

 nected with the coronoid process on the edge of the 

 bone immediately above it. 



In front of this the ramal vacuity — a narrow slit — 

 is usually completely closed by the splenial element. 



The bone now becomes shallower in the vertical di- 

 rection, its superior and inferior borders rounded, 

 while a well-defined gutter for the passage of nerves 

 and vessels marks its entire length. 



As a rule, among the Anatidce the symphysis is 

 rather deep, rounded beneath, and correspondingly 

 concave above, the under side being thickly studded 

 with vascular foramiua. Spatula has a somewhat dif- 

 ferent anterior ending from this, as is shown in Fig. 20. 



In the middle line in front a sort of "nail" is devel- 

 oped like the one found on the superior mandible, 

 though not so strong. The superior ramal margins 

 are continued round this projection, forming its edge, 

 while the spoon like dilatation is insured by the outer 

 ramal sides shelving away from this upper border, so 

 as to face upward and outward rather than directly 

 outward, as they do posteriorly. 



Fig. 20. Mandible of 

 Spatula clypeata; seen 

 from abo\e; adult cT; 

 life size, from the speci- 

 men. 



