AESINOITHEEIUM. 9 



are somewhat triangular in section : the sharp anterior angle is continued down- 

 wards to the border of the nasal opening (PL I. and PI. II. fig. 1 a). The 

 inner face is nearly flat, the posterior is also flattened, while the outer side 

 is rounded. In what may be regarded as an adult female skull the horns are 

 much smaller, more erect, and very irregularly ossified at their tips, which are 

 rounded anteriorly, but terminate posteriorly in an irregular mass of bone. This 

 skull was figured by Mr. Beadnell in his original paper (pis. iii.-v.). The 

 specimen in question is fully adult, for the last molar is well worn, all the 

 sutures are closed, and the prenasal bar fully ossified. In the young the horns 

 are rounded at the summit, where the bone is of a peculiarly fibrous or spongy 

 texture, showing that growth was actively proceeding at this point. The central 

 portion of the horns is occupied by an enormous sinus, the walls being relatively 

 thin, about '5 cm. to 1 cm. in thickness in the adult, and much less in the young. 

 The sinus occupies the bodies of the nasals and frontals and in the latter extends 

 into the small supraorbital horns. Furthermore, it extends back into the parietal 

 and in the old animal even into the base of the lateral prominences of the lambdoidal 

 crest. In the cranial region the sinus is more or less completely divided into a 

 right and left half by a median septum occupying the position of the suture between 

 the parietals. Here the lower table of bone forming the actual wall of the brain- 

 case is very thin, while the upper table is greatly thickened. In the frontal and 

 nasal regions the separation into two lialves is not complete, but there is both in 

 the mid-dorsal , and mid-ventral line a greatly thickened ridge projecting into the 

 cavity of the sinus ; the ventral ridge is the stronger and forms a laterally 

 compressed bar of bone. These main longitudinal thickenings are connected 

 transversely by less prominent, more or less regularly arranged thickenings of 

 the walls, and these again are occasionally united by irregular ridges. In the 

 paired portion of the horns there are only transverse ridges running round the 

 cavity, with some irregular secondary ridges joining them at a few points. The 

 great anterior horns thus consist of comparatively thin bony walls, which are 

 strengthened by a complex system of buttresses, and are further braced against 

 thrusts in the direction of their long axis by the columns resulting from the union 

 of the nasals and maxillae above noticed, and, in the adult, by the prenasal bar. 

 The surface of the horns is marked by a series of shallow grooves running more 

 or less in the direction of their long axis and frequently anastomosing. On the 

 antero-lateral faces of the horns, a little above the nasal opening, there are impressions 

 of blood-vessels (see PL I., h.v.') similar to those described on the frontals. 



The premaxUlce (pmw.J are relatively small bones. The alveolar bolder of each, 

 as usual, bears three incisor alveoli. Of these the first pair is considerably the 

 largest ; they are rounded with a raised border and are separated in the middle 

 line by an interval of about 2'5 cm., in which the edge of the bone is rounded and 



c 



