OSTEOLOGY OF BIRDS 



279 



This description of the cranial base and posterior aspect of the 

 skull in the Spoonbill practically answers for the Mallard and the 

 teals, though, of course, slight differences do exist. 



In Clangula islandica the basis cranii is propor- 

 tionately flatter; the temporal wings less manifest; a separate 

 ridge bounds the fossa for the nerve and arterial foramina ex- 

 ternally, and the condyle is more prominent and its superior median 

 notch very deep. The vault of the cranium is very lofty in this 

 duck, and the ridge bounding the occipital area almost crestlike [see 

 fig. 16, 17]. 



Speaking of the unusual hight of the cranial vault in the Garrot, 

 we find this bird very peculiarly constructed in this particular, for 



Fig. 18 Left lateral view of the skull of Clangula islandica, natural size. 

 a, premaxillary, dentary part; b, its palatine portion; b' , internarial aperture; c, anterior 

 part of left premaxillary; d, dentary of mandible; e, groove for nerves and vessels; 

 f, ramal slit or vacuity; g, articular surface; h, posterior angular process; i, occipital 

 protuberance; j, supraoccipital foramen; k, temporal fossa; /, external lateral aural 

 aperture; m, postfrontal process; n, quadrate; o, pterygoid; p, palatine; q, quadratojugal; 

 r, .jugal; s, maxillary; t, vault of cranium; u, lacrymal; z\ vomer; w, supraorbital 

 depression for nasal gland; x, 'cranio-facial hinge; y, foramen rotundum; z, an inter- 

 orbital vacuity 



not only is the brain case of a size above the average for the group, 

 but a curious and not inconsiderable diploic cavity overlies the whole 

 top of the skull, extending as far forward as the mesethmoid. Here 

 it is interrupted by a pair on either side, one in front of the other, of 

 deep and sharply defined chambers, with their apertures facing di- 

 rectly downward. This condition is not so pronounced in a young 

 female Clangula, a specimen of which I have before me. 



Anatinae have their skulls more or less perfectly permeated by 

 air, and when properly prepared are really structures of great 



