276 



SCIENCE. 



[Vol.. II., No. :!0. 



.■5-0. In tlie Loiip-Fork fauna, some possess toes but 

 1-1. Prior to tbis period no suuh reduction was 

 known, though in the Loup-Fork fauna a very few 

 species were .5-5. Tlirough tills entire series we have 

 transitions steady and constant, from 5-5, to 4-5, to 

 4-4, to 4-3, to 3-3, to 2-2, to 1-1. In tlie Puei-co 

 period there was not a single mammal of any kind 

 which had a good ankle-joint; which had an ankle- 

 joint constructed as ankle-joints ought to he, with 

 tongue and groove. The model ankle-joint is a 

 tongue-and-groove arrangement. In this period they 

 were all perfectly flat. As time passes on we get 

 them more and more grooved, until in the Loup- 

 Fork fauna and the White-River fauna they are all 

 grooved. In the sole of the foot, in the Puerco fauna, 

 they are all flat; but in the Loup-Fork fauna the 

 sole of the foot is in the air, and the toes only are 

 applied to the ground, with the exception of the line 

 of monkeys, in which the feet have not become erect 

 on the toes, and the elephant, in which the feet are 

 nearly flat also, and the line of bears, where they are 

 also flat. As regards the ungulation between the 

 .small hones of the palm and of the sole, there is not 

 a single instance in which the bones of the toes are 

 locked in the lower eocene, as they are in the later 

 and latest tertiary. 



When we come to the limbs, the species of the 

 Puerco fauna have short legs. They have gradually 

 lengthened out, and in the late periods they are 

 nearly all relatively long. 



Coming to the vertebrae as a part of the osseous 

 system, I will mention tlie zygapophyses, or antero- 

 posteiior direct processes, of which the posteiior looks 

 down, and the anterior looks up. They move on each 

 other, and the vertebral column bends from side to 

 side. In the lower forms of mammals they are al- 

 ways flat, and in the hoofed mammals of the Puerco 

 period they are all flat. In the Wasatch period we 

 get a single group in which the articulation, instead 

 of being perfectly flat, comes to be rounded; in the 

 later periods we get them very much rounded; and 

 finally, in the latest forms, we get tlie double curve 

 and the locking process in the vertebral column, 

 which, as in the limb, secures the greatest: strength 

 with the greatest mobility. In the fir.st stages of the 

 growth of the spinal coi'd, it is a notochord, or a 

 cylinder of cartilage or softer material. In later 

 stages the bony deposit is made in its sheath until it 

 is perfectly segmented. 



Now, all the Permian land-animals, reptiles, and 

 batrachians retain this notochord with the begin- 

 nings of osseous vertebrae, in a greater or less de- 

 gree of complexity. There are some in South Africa, 

 I believe, in which the ossification has come clear 

 through the notochord; but they are few. This 

 characteristic of the Pei'mian appears almost alone, 

 — perhaps absolutely alone as regards land-ani- 

 mals. There is something to be said as to the condi- 

 tion of that column from a mechanical standpoint, 

 and it is this: that the cord exists, its osseous ele- 

 ments disposed about it; and in the batrachians re- 

 lated to the salamanders, and the frogs, these osseous 

 elements are arranged under the sheath in the skin 



of the cord; and they are in the form of regular 

 concave segments, very mucli like such segments as 

 you will take from the skin of an orange, — parts of 

 spheres, and liaving greater or less dimensions ac- 

 cording to the group or species. Now, the point of 

 divergence of these segments is on the side of the 

 column. They are placed on the side of the column 

 where the segments separate, — the upper segments 

 rising and the lower segments coming downward. 

 To the upper segments are attached the arches and 

 their articulations, and the lower segments are like 

 the segments of a sphere. If you take a flexible 

 cylinder, and cover it with a more or less inflexible 

 skin or sheath, and bend that cylinder sidewise, you 

 of course will find that the fractures of that part of the 

 surface will take place along the line of the shortest 

 curve, which is on the side; and, as a matter of fact, 

 you have breaks of very much the character of the 

 segments of the Permian batrachia. It may not be 

 so symmetrical as in the actual animal, for organic 

 growth is symmetrical so far as not interfered with; 

 for, when we have two forces, the one of growth and 

 the other of change or alteration, and they contend, 

 you will find in the organic being a quite symmetri- 

 cal result. That is the luiiversal rule. In the cylin- 

 der bending in this way, of course the shortest line 

 of curve is I'ight at the centre of the side of that 

 cylinder, and the longest curve is of course at the 

 summit and base, and the shortest curve will be the 

 point of fracture. And that is exactly what I pre- 

 sume has haijpened in the case of the construction 

 of the segments of the sheath of the vertebral column 

 in the lateral motion of the animal swimming, always 

 on one side, and which, at least, has been the actual 

 cause of the disposition of the osseous material in 

 its form. I have gone beyond the slate of the dis- 

 cussion in calling attention to one of the forces which 

 have probably produced this kind of result. That 

 is the state of the vertebral column of many of the 

 vertebrata of the Permian period. 



I go back to the mammalia, and call attention to 

 the teeth. The ordinary tooth of the higher type of 

 the mammalia, whether hoofed or not, with some ex- 

 ceptions, is complex with crests or cusps. In cutting 

 the complex grinding surfaces we find they have been 

 derived by the infolding extensions of four original 

 cusps or tubercles. They have been flattened, have 

 been rendeied oblique, have run together, have folded 

 up, have become spiked, have descended deeply or 

 have lifted themselves, so that we have teeth of all 

 sorts and kinds, oftentimes very elegant, and some- 

 times very effective in mechanism. In many pri- 

 mary ungulates, the primitive condition of four con- 

 ical tubercles is found. In passing to older periods 

 we find the mammalia of the Puerco period, which 

 never have more than three tubercles, with the ex- 

 ception of three or four species. In the succeeding 

 periods, however, they get the fourth tubercle on the 

 posterior side. Finally, you get a complicated series 

 of grinding or cutting appar.atus, as the case may be. 

 Last, but not least, we take the series of the brain. 

 No doubt the generalization is true, that the primi- 

 tive forms of mammalia had small brains Wfth gnipoth 



