Later in age than Poebrotherium is Protolabis, a Tylopod in which the full number of teeth is still retained; its skull presents no particular changes from the Poebrotherine type; the nasals, however, are somewhat shortened.
Later still in point of time is Procamelus. In this form we have apparently an ancestral stock, whence both Camels and Lamas were derived. The upper incisors are as in existing forms, but the first and second persist for a somewhat longer time. The skull shows two well-marked types of structure; in P. occidentalis
there are more points of likeness to the Lama, in P. angustidens to the Camel. In both, the orbits are completely encircled by bone. The nasals are much shortened. The odontoid process of the axis is still more concave than in Poebrotherium, but not spout-like as in existing forms. This fact shows that the spout-like character of the Camels' odontoid process is not a point of affinity to other Artiodactyles—in fact the occurrence of the same form of odontoid process in Perissodactyles is enough proof of this. We must come to the conclusion that the form is adaptive in all cases. If we were not obliged on palaeontological evidence to come to this conclusion, the structure in question is just one which would be fastened upon as evidence of genetic affinity; for it is a resemblance in a small though distinctive point of structure having no obvious relation to utility. The metacarpals and metatarsals have coalesced to form the cannon bones, though a rudiment of one metacarpal seems to remain. The genera referred to appear to be on the direct line of descent of the modern representatives of the family. But there are other forms which are offshoots of the main stem. Such are Homocamelus, Eschatia, and Holomeniscus. The last two are Pliocene and American; the teeth are much reduced.
C. PECORA.
The Pecora are a group which possess so many characters in common that it is not an easy task further to subdivide them.
In all there are but two functional digits on the feet, and the metacarpals and metatarsals of these are fused. There are no upper incisors, and canines in the upper jaw are not universal, and generally small. Horns are confined to this group of the Selenodontia.[[188]] The premolar teeth are of a simpler form than the molars. The stomach has four chambers, of which two may be regarded as belonging to its cardiac half and two to the pyloric. The former are, in the first place, a large paunch or rumen, followed by a smaller reticulum, so called on account of the network arrangement of the folds of its lining membrane. Connected with the latter, and constituting the first part of the pyloric half of the stomach, is the psalterium or "manyplies," so called on account of the longitudinal folds, like the leaves of a
book, into which its lining membrane is raised. Finally there is the abomasum, out of which proceeds the small intestine. Garrod has observed that the chamber of the stomach which varies most among the Pecora is the psalterium. This chamber is specially large in Bos, and particularly small in the Antelopes Nannotragus and Cephalophus. But its variation relates more especially to the folds of its mucous membrane. These folds are of varying lengths and have a definite arrangement There may be as many as five sets of laminae of regular depths. The most simple psalterium is that of Cephalophus, where there are only two sets of laminae of different sizes, a deeper set and a very much shallower set; this form is termed by Garrod "duplicate." Most common is the "quadruplicate" arrangement, with four sets of laminae of differing depths. In all Pecora the liver is but little divided by fissures.
Fam. 6. Cervidae.—The Deer tribe is a very extensive one, and, with the exception of Africa and Australia, world-wide in distribution.[[189]]
The Deer are absolutely distinguished from all other Ruminant animals by the existence of antlers, which are invariably present in the male sex, save in the aberrant genera Moschus and Hydropotes; in the Reindeer alone are antlers present in both sexes. The general characters of these appendages have been dealt with on a former page (p. [200]), where they are compared to, or rather contrasted with, the horns of the Bovidae. These antlers, so characteristic of the Cervidae, are very variously developed among the members of the family. Thus in Elaphodus the antlers are very small and entirely unbranched. In the Muntjacs, Cervulus, the antlers are hardly larger, but they have a small anterior branch arising from near the pedicel, the "brow tine." In Cariacus antisiensis only one branch, the brow tine, is present, but it is nearly as long as the main stem of the antler, the "beam." In Capreolus capraea the beam bears two tines; in Cervus sika three; in C. duvauceli two of the three tines present bear secondary branches. There are other complications (some of which are illustrated in Figs. 152-157) of the simple antler which culminate in the complex antlers with their expanded "palms" of the Elk and the Fallow Deer.