Of all the discoveries of ancient remains, whether possibly or certainly human, two in particular stand out pre-eminently in marked relief. The specimens thus distinguished are known as the remains of _Pithecanthropus erectus_, on the one hand, and on the other a jaw-bone which is attributed to a human type described (from the locality of the discovery) as _Homo heidelbergensis_. The geological antiquity assigned in each instance is greater than that claimed for any bones acknowledged unreservedly to be human. It is thus clear that a high value attaches to these specimens if they be regarded as documents testifying to the course of human evolution. When the bones are examined, the contrast they provide with all human remains is so marked as to emphasise at once the necessity for a thorough and critical examination of their structure. _Pithecanthropus erectus._ In the case of these bones, the facts are now so widely known and so easily accessible as to render unnecessary any detailed exposition here. The discoveries were made in the years 1891 and 1892 by Professor Dubois[1], who was engaged at the time on an investigation of the remains of various animals found embedded in a river-bank in Java. As is well known, the actual remains are scanty. They comprise the upper part of a skull, part of a lower jaw (which has never been described), three teeth, and a left thigh-bone. [1] The numbers refer to the Bibliography at the end of the volume. Before entering upon any criticism of the results of Professor Dubois' studies, it is convenient to give a general statement of his conclusions. Here we find described a creature of Pliocene age, presenting a form so extraordinary as hardly to be considered human, placed so it seems between the human and simian tribes. It is Caliban, a missing link,--in fact a Pithecanthropus. With the erect attitude and a stature surpassing that of many modern men were combined the heavy brows and narrow forehead of a flattened skull, containing little more than half the weight of brain possessed by an average European. The molar teeth were large with stout and divergent roots. The arguments founded upon the joint consideration of the length of the thigh-bone and the capacity of the skull are of the highest interest. For the former dimension provides a means of estimating approximately the body-weight, while the capacity gives an indication of the brain-weight. The body-weight is asserted to have been about 70 kgm. (eleven stone) and the brain-weight about 750 gm. And the ratio of the two weights is approximately 1/94. The corresponding ratios for a large anthropoid ape (Orang-utan) and for man are given in the table following, thus: Orang-utan 1/183 _Pithecanthropus erectus_ 1/94 Man 1/51 The intermediate position of the Javanese fossil is clearly revealed.