Important as these are, they are not the points which the ethnologist most looks to. Although the colour of the skin and eyes and the texture of the hair may be determined by external influences, the real reasons for the differences of _outline_ lie in the differences of the skull and the bony parts of the face: and as, in addition to this, the skull is the receptacle of the brain, and the brain is the organ wherein the human species most differs from others, anatomists have long been in the habit of determining the different varieties of the human race, by the difference in the conformation of their skulls. With this view, the particular bones of most importance are the following:-- _The Frontal bone, forming the forehead._--The more the frontal bone retires, the lower is the forehead, and the more prominent the face. The more it is vertical or arched, the more the brain seems to be in superposition _over_ the face; rather than lying _behind_ it. By drawing one line from the opening of the ear to the base of the nose, by drawing a second from the most prominent part of the forehead to the insertion of the teeth, and by measuring the inner angle at which these two lines bisect each other, we have the famous facial angle of Camper; in other words, we have a measure for the extent to which a forehead is retreating or vertical. _The Occipital bone._--This forms the back of the head. The distance between the frontal and occipital bones is the occipito-frontal diameter. It constitutes the _length_ or _depth_ of the head, in contradistinction to its _breadth_. _The Parietal bones, forming the sides of the skull._--The distance between the two parietal bones is the parietal diameter. It constitutes the _breadth_ of the skull, in contradistinction to its _length_ or _depth_. The ratio between these two diameters has been most studied by Professor Retzius, of Stockholm. Nations where the development is in the occipito-frontal diameter are called _dolikhokephalic_.[1] Nations where it is in the _parietal_ diameter are called _brakhykephalic_.[2] _The Zygoma._--Formed by the union of two processes, one from the malar, and one from the temporal bone, and enclosing a space, within which the muscles pass from the temporal bone to the lower jaw. It constitutes the ridge that can be felt through the skin, between the cheek-bone and the ear. When the zygomatic space is large, the arch of the zygoma itself projects laterally outwards. _The Malar bones, i.e. the cheek-bones._--It is unnecessary to say that the prominence of the cheek-bone affects the physiognomy. When, over and above this prominence, the zygoma has a lateral and outward development, the breadth of the face becomes remarkably and characteristically broad and flat. It is upon the effect of a great zygomatic development on the form of the skull that Prichard has founded one of his primary divisions. [Illustration: Fig. 2.] [Illustration: Fig. 3.]