The criminal skull does not exhibit any marked characteristics of size and shape. Generally speaking, it tends to be larger or smaller than the average skull common to the region or country from which the criminal hails. It varies between 1200 and 1600 c.c.; _i.e._, between 73 and 100 cubic inches, the normal average being 92. This applies also to the cephalic index; that is, the ratio of the maximum width to the maximum length of the skull[1] multiplied by 100, which serves to give a concrete idea of the form of the skull, because the higher the index, the nearer the skull approaches a spherical form, and the lower the index, the more elongated it becomes. The skulls of criminals have no characteristic cephalic index, but tend to an exaggeration of the ethnical type prevalent in their native countries. In regions where dolichocephaly (index less than 80) abounds, the skulls of criminals show a very low index; if, on the contrary, they are natives of districts where brachycephaly (index 80 or more) prevails, they exhibit a very high index. =SKULL FORMATION FIG. 2 FIG. 3= In 15.5% we find trochocephalous or abnormally round heads (index 91). A very high percentage (nearly double that of normal individuals) have submicrocephalous or small skulls. In other cases the skull is excessively large (macrocephaly) or abnormally small and ill-shaped with a narrow, receding forehead (microcephaly, 0.2%). More rarely the skull is of normal size, but shaped like the keel of a boat (scaphocephaly, 0.1% and subscaphocephaly 6%). (See Fig. 2.) Sometimes the anomalies are still more serious and we find wholly asymmetrical skulls with protuberances on either side (plagiocephaly 10.9%, see Fig. 3), or terminating in a peak on the bregma or anterior fontanel (acrocephaly, see Fig. 4), or depressed in the middle (cymbocephaly, sphenocephaly). At times, there are crests or grooves along the sutures (11.9%) or the cranial bones are abnormally thick, a characteristic of savage peoples (36.6%) or abnormally thin (8.10%). Other anomalies of importance are the presence of Wormian bones in the sutures of the skull (21.22%), the bone of the Incas already alluded to (4%), and above all, the median occipital fossa. Of great importance also are the prominent frontal sinuses found in 25% (double that of normal individuals), the semicircular line of the temples, which is sometimes so exaggerated that it forms a ridge and is correlated to an excessive development of the temporal muscles, a common characteristic of primates and carnivores. Sometimes the forehead is receding, as in apes (19%), or low and narrow (10%).