726 THE POPULAR SCIENCE MONTHLY. 



tricht beds, to which we have referred above, as well as in the method 

 of replacement, for some of the teeth preserved have the crowns of their 

 successors implanted in cavities in their fangs. This peculiarity in the 

 manner of teeth-shedding is characteristic of some reptiles, each of 

 whose teeth is merely a hollow cone tilled in the interior with a soft 

 pulp which supplies the material for the external bony layer. When 

 the tooth becomes worn and useless, a new one is formed beneath the 

 shell of the first by the pulp in the interior, which gradually ousts the 

 old from its socket. In addition to these, the hesperornis possessed 

 other reptilian characters. While the formation of the spinal column 

 in the neck and back is of the true avian type, the structure of the 

 tail, where there have been discovered no fewer than twelve segments, 

 is very peculiar, and differs entirely from anything hitherto seen 

 in birds. The bones of its middle and posterior portions have very 

 long and horizontally flattened processes which prevent all motion in a 

 lateral direction : a peculiarity from which we may certainly infer that, 

 like the beaver's, this appendage was moved vertically, and doubtless 

 was an efficient aid in diving, perhaps compensating for want of wings, 

 which the penguins use with such wonderful dexterity in swimming 

 under water. The last three or four bones are firmly united together, 

 forming a flat terminal mass analogous to, but quite unlike, the 

 " ploughshare " bone of modern birds. 



Here, again, is another form half doubtful whether to assume the 

 reptilian or the avian garb, a protestant against the hard and fast 

 lines within which the various groups of the animal kingdom have 

 hitherto been confined. The hesperornis certainly approaches the ich- 

 thyornis so far as to come under the new sub-class instituted for the 

 reception of that bird ; but, inasmuch as it differs in having its teeth 

 not in sockets but set in a groove, and since, rejecting the conservative 

 bi-concavity in the matter of spinal segments, it has adopted a newer 

 and more high-class " cut," it has been necessary to give to each the 

 honor of heading a separate section. 



Though no living bird has so long a tail as this bird-of-the-dawn, 

 yet there was in 1862 disinterred from the lithographic slates of Solen- 

 hofen part of the skeleton of a feathered biped the archasopteryx (the 

 existence of which was foreshadowed by the discovery of a feather the 

 year before), exhibiting in most of the bones preserved the marks of a 

 true bird. In the length of its tail, however, it is peculiar. This ap- 

 pendage contains the enormous number of twenty distinct bones grad- 

 ually decreasing in size to the last, and each supporting a pair of quill- 

 feathers. To the skeleton no head is attached ; but a portion of a 

 small separate jaw on the same slab has been the subject of much con- 

 troversy as to whether it belongs to the accompanying bones or not. 

 Hermann von Meyer, the illustrious anatomist and paleontologist, holds 

 that there can be little doubt but that they are parts of one and the same 

 skeleton. If this be so, these remains belonged to a toothed bird ; and 



