The compressive strength of single human osteons has been investigated in specially prepared samples using a microtesting machine equipped with a microwave micrometer. The main conclusions which can be drawn from our results are: (1) In agreement with Gebhardt's theories the ultimate compressive strength is greatest for osteons having transversally oriented fiber bundles, lowest for osteons having longitudinally oriented fiber bundles, and intermediate for osteons whose fiber bundles change direction in successive lamellae through a n angle of about 90". Nearly 60 years ago the German investigator W. Gebhardt ('06) developed a theory designed to explain the relationship between structure and mechanical properties of osteons. As no suitable technique for performing investigations on isolated osteons was then available, Gebhardt founded his theory on macroscopic metallic models in which bone collagen and crystallites were represented by steel wires.During the last few years we have carried out a series of investigations on the tensile properties of single osteons (Ascenzi and Bonucci, '64, '65, '67; Ascenzi, Bonucci and Checcucci, '66). As it was practically impossible to isolate a whole osteon, the studies in tensile strength were done using portions of longitudinally sectioned units. For this purpose the dissection technique described by Ascenzi and Fabry ('59) was applied. The apparatus used for measuring the variations in length of the osteons subjected to tensile stress was a microwave extensimeter based on cavity and pulse techniques. This apparatus was developed at the Physics Institute of the University of Pisa by Gozzini and co-workers (see Battaglia, Bruin and Gozzini, '58).Recently further attempts have been made by us to test the compressive properties of cylindrical samples corresponding approximately to the middle portion of single osteons. The aim of this report is to present the results of these investigations. MATERIAL AND METHODPreparation and selection of samples. The osteon, when fully formed, is an irregularly cylindrical and branching structure a few millimeters in length and usually oriented in the long axis of the bone.

The ultimate tensile strength and modulus of elasticity of individual osteons from human and ox compact bone were determined with a specially designed microwave extensimeter. The results were related to the degree of calcifkation and the orientation of collagen fiber-bundles in successive lamellae of the osteons. The following conclusions were made: (1) When osteon specimens are dried, their tensile strength and modulus of elasticity increase, while their percent elongation under tension falls.(2) In the osteon samples tested wet, the degree of calcification induces an increase in the modulus of elasticity with additional amounts of calcium salts. (3) The modulus of elasticity in tension of the organic matrix corresponds to that of collagen. ( 4 ) In the osteons having a marked longitudinal arrangement of bundles of fibers in successive lamellae, the ultimate tensile strength and modulus of elasticity seem greater and the percentage elongation under tension seems lower than in osteons whose bundles in successive lainellae change through an angle of about 90". (5) The tensile properties of osteons seem independent of the age of the subject. (6) Human and ox osteons reveal the same tensile behavior. (7) The tensile stress-strain curves show that, even at the level of single osteons, bone behaves like a complex material, which, according to Sedlin, can be represented by a Hooke body linked in series to a Kelvin body.In the last two decades, there has been an increased interest in problems concerned with the mechanical properties of bone (cf. Evans, '57; Sedlin, '65).At the present time, the lack of any quantitative studies of the micromechanical properties of isolated osteons has induced us to investigate the tensile strength of samples obtained by dissection from Haversian systems. In a previous paper, the results of research on the ultimate tensile strength of the same units were given (Ascenzi and Bonucci, '64). The aim of this paper is to present the definitive results of a quantitative investigation of the tensile deformation of single osteons from human and ox femoral shafts using a specially designed microwave extensimeter.2 MATERIALS AND METHODSAs discussed in a previous paper (Ascenzi and Bonucci, '64), it appears very difficult at the present time to isolate samples corresponding to a whole osteon in order to test tensile properties. For this reason, the present tensile strength studies were made on samples corresponding to portions of longitudinally sectioned osteons.Longitudinal sections, 20-50 p in thickness, were prepared from femoral shafts by grinding them on glass plates. Special care was taken to avoid heating the material. The samples were taken from longitudinally sectioned osteons using the dissection technique described by Ascenzi and Fabry ('59) and Ascenzi and Bonucci ('64). With this technique it was easy to prepare samples of the desired shape ( fig. l a ) .A region with parallel sides was isolated from the middle portion of half a longitudinally sectioned osteon, as seen in figure ...

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The human fossil evidence unequivocally pertaining to the first inhabitants of Europe at present includes the sample from Atapuerca-TD6 (Spain) and the incomplete adult calvaria discovered near Ceprano, in Southern Latium (Italy). On the basis of regional correlations and a series of absolute dates, the age of the Ceprano hominid is estimated to range between 800 and 900 kilo-annum (ka). In addition, the association with archaic (Mode 1) Paleolithic findings from the same area is suggested. After the completed reconstruction of the calvaria, we present here a new study dealing with the general and more detailed aspects of the morphology displayed by Ceprano, in comparison to fossil samples ranging between Early and Middle Pleistocene. According to our results, cranial features indicate that Ceprano represents a unique morphological bridge between the clade Homo ergaster͞erectus and later Middle Pleistocene specimens commonly referred to Homo heidelbergensis (and͞or to Homo rhodesiensis), particularly those belonging to the African fossil record that ultimately relates to the origin of modern humans. In conclusion, given its geographical, chronological, and phylogenetic position, an attribution to the species Homo antecessor is considered, although the sample from Atapuerca-TD6 is not directly comparable to Ceprano. Alternatively, a new species-ancestral to later European and African hominines-should be named to accommodate such a unique fossil specimen.