58 



PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



It is generally assumed that the fourth tarsalc of modem mammals is a compound 

 bone formed by the fusion of the fourth and fifth tarsalia. There is no embryological 

 evidence of such fusion, and with SewartsefT (Anat. Anz., 1904, p. 483) and Baur I believe 

 that the fifth tarsale has entirely disappeared in all modern vertebrates. It is an actual fact 

 that in some Permian reptiles the fifth tarsale is gone, not fused, but disappeared as a bone. 

 I am not one of those who must find in the human skeleton distinct ossificatory or even 

 embryological evidence of every lost bone that has existed in ancestral forms. In some cases 

 it is quite certain that bones do fuse; the temporal and frontal bones of mammals, to say 

 nothing of the opisthotic, etc., are sufficient evidences of the fusion not only of cartilage 

 bones, but membrane bones as well. But, in many cases, it is equally evident that bones 

 actually disappear. Possibly they remain as potential or latent elements, as mere germs, 

 which under stimulation in later forms may develop sporadically into a semblance of their 

 original forms, such as some of the accessory or anomalous bones found in the human 

 carpus and tarsus, the centrale carpi or the cuboides secundarium for instance. And yet. 

 it would seem tliat we are going a long way back, to the Trias or Pennian perhaps, to find 

 the normal functional prototyp)es of some of these germs. Indeed, if we must find the 

 functional antecedents of all the anomalous bones found in the human carpus and tarsus 

 we shall have to go back quite to the Stegocephalia, if not the fishes. It seems to me more 

 probable that many of such anomalies are to be explained by duplication, by the splitting 

 or division of normal germs, as we know is quite possible. 



RESTORATION. 



The accompanying restoration, made with painstaking care (fig. 36), and the 

 mounted skeletoji as shown in the photographic illustration (pi. i, fig. 3) have very 

 little that is conjectural or even doubtful. The spines of the posterior lumbar, 



^^^IS 



Fig. 36. — Skeleton of Ophiacodon mirus Marsh as restored. About one-tenth natural size. 



sacral, and the basal caudal vertebrae are unknown ; they are shown in the drawing by 

 barred outlines ; in the mounted skeleton they are restored in light-colored plaster-of- 

 paris. Enough caudal vertebras from different parts of the tail are known to render 

 it certain that it was very much like that of Varanosaurus, that is, slender and nearly 

 as long as the presacral region. It was doubtless composed of about fifty-five ver- 

 tebrae, of which about twenty are wanting. The chevrons are represented by frag- 

 ments only. The scapula is placed very nearly as the left one was found lying in the 

 specimen. The right scapula lay immediately over the left one, save that it had been 

 pushed downward a short distance. The curvature of the vertebral column in the 

 cervical and dorsal region as found, and as shown in pi. i , fig. 2, which is a photograph 

 of a cast of the specimen as it lay in the matrix, is perhaps a little exaggerated, though 

 doubtless normal, since all the vertebrae lay in immediate contact and without notice- 

 able displacements. The curves, however, are probably not those often assumed in 

 life ; they have been reduced a little in the figure. The skull in the mounted skeleton 



