AESINOITHEEIUM. 



The supraoccipital (soc), as already mentioned, is excluded from the foramen 

 magnum. It forms the whole of the upper part of the sloping occipital surface, 

 which is bounded above by the thickened, rugose, and very prominent lambdoidal 

 crest [s.c). This seems to be situated along the junction of the supraoccipital and 

 the parietals, though it is impossible to determine precisely which is the line of 

 union, since even in the youngest specimens the suture is closed. In the middle 

 line there is a prominent ridge for the attachment of the ligamentum nuchce, and 

 on either side of this the surface is greatly roughened, like the surface of the 

 lambdoidal crest. 



The parietals (pa.) are not only fused with the supraoccipital, but also with one 

 another in the youngest specimens available for examination. In the immature 

 skull figured on PL III. fig. 2 there is, in the middle line of the skuU-roof, 

 a small foramen, which opens into the sinus occupying this part of the cranial 

 wall and is probably a remnant of the sagittal suture. This opening is absent in 

 other specimens, and therefore cannot be regarded as of importance. The parietals 

 form the anterior portion of the lambdoidal crest, in front of which they constitute 

 the skull-roof, which is nearly flat from side to side, and slightly concave from before 

 backwards. Laterally they turn downwards almost at right angles, and help to form 

 the side-walls of the skull, their lower edges meeting the squamosals in a nearly 

 straight suture, which runs downwards and forwards (PL III. figs. 1, 2 a). The 

 upper edge of this lateral region of the parietals is sharply defined by the strongly- 

 marked ridge, which forms the upper limit of the temporal fossa and is continued 

 forwards on the frontals as far as the orbits. In the adult the fronto-parietal suture 

 is closed, but in the young (PL III. fig. 2) it can be seen that the parietals extend 

 forwards in the middle line between the small frontal horns. Immediately behind 

 these the fronto-parietal suture turns forwards to the supratemporal ridge, after 

 crossing which it turns downwards and somewhat backwards, running down to 

 join the parieto-squamosal suture. 



The squamosal (sq.) is a large and complicated bone which takes a considerable 

 share in the formation of the side-wall of the cranium. Its sutures with the' 

 parietal and exoccipital have already been referred to. It cannot be determined 

 whether or not it had any contact with the supraoccipital, but probably its upper 

 posterior angle, which helps to form the large lateral occipital prominence, united 

 with that bone at least for a short distance. Beneath this prominence the 

 surface of the bone is roughened and raised into a ridge, which in the adult 

 skull forms a strong, backwardly-directed, hook-like process (text-fig. 1, pr.) for 

 the attachment of muscle, situated above and rather behind the opening of the 

 external auditory meatus (Pis. I., II. fig. 1, e.a.m.). Ventrally the bone is produced 

 downwards into a broad post-tympanic flange {pty.), which terminates below in a 

 blunt point and is supported posteriorly by the downward process of the exoccipital 



