. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. Pollex /) -Sled Fig. Primitive ungulate foot.—Lims of vertical cleavage on either side of tin middle toe, III. Spreading of toes would cause separation of tbe (^ Recent ungulate foot.—No inics of vertical cleavage. All joints lirokcii by ciilargeiiient of scaphoid, iincifonu, and , tlie bones reseiving greatest impact in walking. Lateral "toes, 1, ^?, ilegciicrate. a very limited degree, plastic and capable of chan
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. Pollex /) -Sled Fig. Primitive ungulate foot.—Lims of vertical cleavage on either side of tin middle toe, III. Spreading of toes would cause separation of tbe (^ Recent ungulate foot.—No inics of vertical cleavage. All joints lirokcii by ciilargeiiient of scaphoid, iincifonu, and , tlie bones reseiving greatest impact in walking. Lateral "toes, 1, ^?, ilegciicrate. a very limited degree, plastic and capable of change of form. Ex lu/pothcsi, it is not the growth, but the reaction tendency which pro- (hu^es the growth, which is transmitted. The evolution of the teeth, therefore, falls into the same category as bone.* In the accompanying figures I have epitomized the slow transformation of the single-fanged conical reptilian tooth, such as we see in the serpents, into the low- crowned human grinder. We now know all the transition forms, so that we can homologize each of the cusps of the human molar with its varied ancestral forms in the line of descent. For example, the anterior lingual or inner cusp of the upper true molars traces its pedigree back to the reptilian cone. The anterior triangle of cusps, or trigon, seen in the mesozoic mammalia and persisting in the first inferior true molar of the modern dog, is still seen as the main i)ortion of the crown of the human upjier molars {pr, pa, me). To this was added, ages ago, the * See especially tbe papers of Ryder, Cope, and the writer, "Evolntioii of Mam- malian Molars to and from the Tritubercular Type," American Naturalist, Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Smithsonian Institution. Board of Regents; United States National Museum. Re
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