Vol. 69.] THE HTHIAN SKULL, ETC. FE03I PILTDOWN. 131 



the insertion of a powerful masseter muscle (ma.). The horizontal 

 portion, or body of the mandibular ramus, measures only about 

 27 mm. in depth behind, but must have become a little deeper 

 forwards. External to the first and second molars there is the 

 usual prominent oblique ledge (6.) for one of the origins of the 

 buccinator muscle ; but this is the only feature visible on the outer 

 face, a large flake of bone behind the position of the mental foramen 

 having been lost when the anterior part was broken. Seen from 

 within, the ascending portion of the ramus is remarkable for the 

 thickening of its anterior margin, to provide a large surface (t.) for 

 the insertion of the temporal muscle as far downwards as the 

 alveolar border. A strengthening ridge extends downwards and 

 forwards from the articular condyle to the lower part of the sharply- 

 defined inner edge of the temporal surface. Below and behind this 

 the large dental foramen (d.) occurs, though its shape is altered by 

 accidental breaking; and still a little lower there is the slight impress 

 of the mylohyoid groove (m.g.). Near the angle (i.pt.) might 

 be expected a roughness for the insertion of a powerful internal 

 pterygoid muscle ; but the bone bears only slight irregularities and 

 it is very little curved inwards. Farther forward the inner face of 

 the ramus is curiously smooth, the origin of the mylohyoid muscle, 

 which forms so conspicuous a ridge in man, being not marked 

 even by a faint line. 



The great width of the temporal insertion, the situation of the 

 mylohyoid groove behind rather than in line with the dental 

 foramen, and the complete absence of the mylohyoid ridge are all 

 characters of the mandible in apes, not in man. It is, therefore, 

 very interesting to note that as the ramus curves round to the 

 symphysis (s.) its lower margin exhibits an increasingly wider 

 flattening, which begins beneath the second molar, slopes upwards 

 and outwards, and ends in front in a strongly retreating chin. 

 The inner edge of this flattening is sharply rounded, and at the 

 symphysis itself the inner face of the jaw is so much depressed in 

 its lower part that the bone here has the form of a nearly horizontal 

 plate or flange, closely similar to that found in all the apes. The 

 genio-hyo-glossal and genio-hyoid muscles, in fact, must have had 

 their origin in a deep pit, as in the apes ; while the digastric can 

 only have been inserted on the edge of the bony flange, instead of 

 extending far over the lower border as in man. The absence of 

 the upper part of the symphysis in the fossil is therefore particu- 

 larly unfortunate, and there is ample scope for speculation as to 

 the precise shape of the bony chin and the extent of the anterior 

 part of the alveolar border. The fractured end does not even, 

 suffice to determine whether or not the part preserved reaches the 

 middle line ; it merely shows that the walls of the jaw are thin, 

 and that the inner tissue must have been coarsely cancellous. As, 

 however, the whole of the bone preserved closely resembles that of 

 a young chimpanzee, it seems reasonable to restore the fossil on 

 this model, and make the slope of the bony chin intermediate 

 between that of the adult ape and that of Homo heidelbergensis. 



