279 



is bj ineatis of liorizoiihil sections, passing tliroiigli the middle of 

 the orbits. In fig. 1 such a section is sketclied ihrongli the skull of 

 a 3'oniig Gorilla child, in fig. 2 through that of an adult male individual. 



In the lateral wall of the orbit iu the infantile skull two parts 

 may be distinguished, an anterior one which borders the orbit 

 outwardly and forms the free outei- wall of the orbit, and a posterior 

 one forming a partition between the orbit and the fossa media (»f 

 the cranial cavity. Between these two parts the lateial wall of the 

 cerebral cranium is connected with the lateral wall of the orbit. 

 This arrfvngement implies that the cranial cavity pailly extends 

 laterally of the orbit, in other words that this cavity partly enters 

 into the Cavum cranii, so that there exists a commoji partition-wall 

 between the Cavum orbitae and the Oavum cranii. [J[)wards in the 

 direction of the roof of the orbit this partition-wall between the 

 two cavities becomes larger, as the cranial wall frontally uiore and 

 more joins the supra-orbilal ridge. The free exterior wall thus 

 becomes smaller and is entirely lacking near the roof of the orbit 

 in the youthful Gorilla skull, as the cranial wall is attached to the 

 orbital roof along the supra-orbital arch. Thus the whole orbital 

 roof has become the partition between this cavity and the C-avum 

 cranii. This means that in (he infantile Gorilla the orbits lie entirely 

 under the cranial cavity. 



How is this in the adult skull? 



It appears from fig. 2 that now on the lateral wall of the orbit 

 the just-described two parts can no longer be distinguished; the 

 posterior intracranial part has disappeared, since the lateral wall of 

 the skull is attached as far backward as possible to the lateral wall 

 of the orbit. The whole lateral wall has become an outer w^all. 

 From a topographical viewpoint this means that the orbit no longer 

 enters into the cranial cavity, but has come to lie before it. This 

 conclnsion is confirmed by a closer examination of the orbital roof. 

 In the infantile skull the frontal wall of the cranial cavity is 

 attached to the orbital roof along the circumference of the orbit, 

 which means that the whole roof of the orbit forms a partition 

 between the cranial and orbital cavities and does not form a free 

 exterior wall. In the adult individual, on the other hand, the cranial 

 roof is attached to the orbital roof very much towards the back, 

 as is seen from fig. 3, representing a sagittal section through the 

 orbit of an adidt Gorilla. The roof of the orbit hns here for the 

 greatei' part become a free exterior wall. 



From this short comparison it already appeal's that the topogra- 

 phical relations of the orbit with regard to the cranial cavity are 



