cl, clavicle; cv, cervical vertebræ; d, dorsal vertebræ; fb, fibula; fm, femur; h, humerus; hx, great toe, or hallux; l, lumbar vertebræ; mc, metacarpals; mt, metatarsals; ph, phalanges, or finger- and toe-bones; pv, pelvis; px, thumb, or pollex; r, radius; s, sacral vertebræ; sc, scapula; sk, skull; tb, tibia; ts, tarsus; u, ulna.
In the wall-case on the opposite (north) side of the bay the study of the skeleton of Mammals is continued by illustrations of the structure of the limbs. At the top of the case is a diagram showing the correspondence of the hand and the foot in their complete typical form, with the names applied to the different bones. The series of specimens below shows the principal deviations actually occurring from this typical condition, which, as may be seen, is very nearly preserved in the human hand. One series shows some of the stages of modification for special purpose (specialisation) by which a typical five-fingered hand becomes converted into the single-toed fore-foot of the Horse; while another series ends with the fore-foot of the Ruminants, sometimes, but erroneously, called a “cloven hoof,” in which only two toes remain. Similar changes are shown in the toes of the hind-foot, illustrating the same common plan running through infinite modifications in detail, enabling the organ to perform such a variety of purposes, and to exhibit such diversity of outward appearance. The existence of this common plan is now generally regarded as due to inheritance from a common ancestor.
Teeth of Mammals.
The central case of the bay contains a collection illustrating the principal characters of the teeth of Mammals. Its inspection should commence at the north-east corner, where the visitor will find himself after completing the survey of the specimens of skeletons in the wall-cases. In the first division are placed specimens showing the general characters of teeth, their form, the different tissues of which they are composed, the two great types of dentition in Mammals, homœodont and heterodont,[5] the names and serial correspondence of the different teeth, and their development and succession. The principal modifications of teeth according to function are next shown by examples of forms adapted for fish-eating, flesh-eating, insect-eating, grass-eating, etc. The remainder of the case is taken up by examples of the dentition of the families of Mammals arranged in order, and prepared so as to display not only the shape of the crowns, but also the number and character of the roots by which they are implanted.
Bay II. Classification of Mammals.
In bay No. II the two wall-cases contain a collection arranged to show in a serial manner the orders and sub-orders of existing Mammals, by examples selected to illustrate the predominating characters by which these are distinguished. A brief popular account of the characteristics of the group, and a map showing its geographical distribution, are placed with each. This is intended to serve not only for an introduction to the study of the class by visitors to the museum, but also as a guide to a method of arrangement which may be adopted in smaller institutions.
Among the illustrations of the order Primates is placed the skeleton of a young Chimpanzee dissected by Dr. Tyson, which formed the subject of his work on the “Anatomy of a Pigmie,” published in 1699, the earliest scientific description of any Man-like Ape.
Skin of Mammals.
The central case of this bay contains illustrations of the outer covering or skin and its modifications in the class of Mammals, divided into the following sections:
1. Expansion of skin to aid in locomotion, as the webs between the fingers of swimming and flying animals, the parachutes of flying animals.