OF COLYMBUS TORQUATUS. 135 



cavity of which is parallel with and corresponds to the concavity of the superior margin of 

 the orbit ; the convexities of the two meet on the median line, where they are separated 

 by a longitudinal ridge. The bottoms of these semilunar grooves are pierced with nu- 

 merous minute foramina. At the anterior extremity of each is a large oval foramen, 

 which transmits to the mucous membrane of the nasal passages the duct of the " nasal " 

 glands which lie in these depressions; the secretion of which moistens and lubricates 

 the pituitary membrane. Posteriorly, on the superior surface of the frontal, there is 

 formed by the divergence of these two nasal fossa 1 , and by the crests which form the 

 anterior boundary of the parietal fossa?, a smooth, diamond-shaped, elevated tablet of 

 bone, — almost the only part of the surface of the skull over which the skiu is directly 

 superimposed. 



The chief noticeable feature on the under surface of the bone is the continuation for- 

 ward of the osseous canal through which the olfactory nerves escape from the cranium, as 



deep well-marked canal, spreading out anteriorly into a still deeper and larger oval fossa. 

 This fossa occupies part of the frontal bone, but still more of the ethmoid ; external to the 

 fossa is the foramen opening into the beds for the nasal glands, with a groove running from 

 the anterior edge of the foramen into the nasal passages, just along the inside of the root 

 of the lachrymal bone. 



Ethmoid. This is little more than a thin vertical lamina, placed in the median line, its 

 superior margin anchylosed with the inferior surface of the frontal ; its inferior margin sim- 

 ilarly united with the long, projecting, basilar process of the sphenoid ; its sides forming 

 anteriorly what there is of an imperfect inter-orbital septum. Its posterior edge is thin 

 and sharp, and forms the anterior margin of the large circular opening between the orbits. 

 Its anterior margin spreads out superiorly so as to become of considerable width where it is 

 fused with the frontal ; below it is deeply concave, running forward some distance, with a 

 pointed extremity. The sivperior part of the lateral surface of the ethmoid is hollowed 

 into a shallow fossa for the olfactory nerve, as already mentioned. There is nothing to cor- 

 respond with our cribriform lamella, nor with the spongy convolutions of the lamellae 

 of bone which so preeminently characterize this bone in mammalia. It still, however, per- 

 forms the ordinary functions of separating the orbits from each other, and the nasal from 

 the ophthalmic cavities, and of supporting the ramifications of the olfactory nerves. 



Bones of the Face. 



The facial bones, like the majority of the cranial, are in adult life anchylosed more 

 or less completely with each other ; the complex osseous structure thus formed having, as a 

 unit, slight motion with the cranial bones, by means of the fronto-maxillary, pterygopala- 

 tine, and tympano-malar articulations. Owing, however, to their peculiar form, the precise 

 line of anchylosis can in most cases be more readily detected than in the bones forming the 

 cranium. All the bones of the human face are repeated, with, it is true, exceedingly diverse 

 shapes, but yet so markedly as to give rise to no difficulty in homologizing them ; but 

 the intermaxillary bone, although fused with the supramaxillary as in man, in birds forms the 

 most prominent and important element of all, — preponderating vastly over the superior 

 maxillary proper. 



Lachrymal. From its position and connections this bone would seem rather to apper- 

 tain to the cranial than the facial group. It is a thick, stout process of bone, five eighths of 



MEMOLKS BOST. SOC. MAT. HIST. Vol. I. Pt. 2. 35 



