7\ 



PLATANISTA. 511 



ing backwards, outwards and sKghtly inwards from the base of the former there is 

 another smaller plate, the temporal, which forms the internal surface of the tem- 

 poral fossa. 



The cerebro-nasal plate when viewed from the cerebral surface is almost quadran- 

 gular, and in young skulls the two original halves of the bone can be detected 

 (PL XL, fig. 1). In that period of its history it is almost vertical, the most anterior 

 portion of the cerebral lobes being lodged in two deep concavities in the upper 

 tw^o-thirds, separated from each other by a moderately developed, internal, vertical 

 crest ; but in aged skulls, the internal surface of the frontal has an upward and 

 backward direction and the concavities for the cerebral lobes are perforated by 

 numerous foramina. In two skulls, I noted a deep pit in the upper part of the left 

 cerebral fossa close to the w^eU- developed, vertical crest, and opposite to it on the 

 other side of the crest a smaller pit. These pits are probably due to the presence 

 on the sm^f ace of the brain of cystic parasites, which, pressing against the skull, pro- 

 duce absorption of its w^alls (?) In one brain the surface bore numerous cysts, which 

 in some cases had corresponding depressions in the skull. In a nearly adult female 

 skuU of which I have made a vertical section through the posterior extremities of 

 the frontals, a large well-defined sinus occurs on the left side ; while the corre- 

 sponding position of the opposite side is filled up with finely cancellated tissue ; 

 in young skulls, however, there are no traces of these sinuses. 



The anterior sm^face of the vertical plate presents a prominent nodose-like rido'e, 

 bearing on the sides of its upper end the minute nasals. It is continuous with the 

 nasal septum, but has a strong twist to the left, which confers on the right side of 

 the plate a longer surface than on the left. The sides of this aspect of the plate 

 are defined by the orbitotemporal wings, and below by the orbitosphenoid which is 

 invested by the alar processes of the vomer. At the junction of the orbitosphenoid 

 and parietals, in young skulls, there is an elongated fissure or imperfection of ossifi- 

 cation internal to where the sphenoidal fissure opens on the anterior surface of the 

 united bones. The orbitotemporal plates differ in form, the right having a straight 

 anterior margin, while the left is outwardly curved in the upper first-half of its 

 extent owing to the sinistral distortion of the skull. They are deeply concave from 

 above downwards and forwards ; and their lower extremities, which are thin triangu- 

 lar plates directed downwards, forwards and slightly inw^ards, are traversed by the 

 optic canals ; a small portion of their posterior margin constituting a part of the 

 upper boundary of the pterygomaxillary fissure. The inner surface of these parts 

 of the orbitotempoml plates presents a rather broad but shallow furrow, which ter- 

 mmates in the orbit and along which the nerves and blood vessels pass ; and below it 

 are two small grooves, along which branches of the second or median branch of the 

 trigeminal pass into the maxillary to appear on the front aspect of that bone. At 

 the inner end of the first-mentioned fissure and on the inner wall of the canal-like 

 continuation of the sphenoidal fissure, there is a minute orifice, the opening of the 

 orbitosphenoid portion of the optic canal. So far the two inner branches of the 

 fifth nerve lie in that canal, and at this point two nerves from the most external 



