280 



Fig. 3. 



verj different in llie }Oimg and the adult Gorilla. This difference 

 may be briefly summarised as follows: in the ^oung individual the 

 oibit for the greater part enters into the Cavum cranii, in the adult 



individual it lies before the cranial 

 cavity. So there is a forwaid dis- 

 placement during growth, caused by 

 lengthening of the orbit in a forward 

 direction only. By the aid of figs. 

 1 and 2 this can easily be pi-oved 

 if the Septum orbitale is particularly 

 kept in view. In both figures the sec- 

 tion passes exactly above the Lamina 

 cribrosa, i. e. through the anter- 

 ior extreme part of the cranial 

 cavity. 



In the septum orbitale of I lie infantile skull three parts may be 

 distinguished, a middle one, formed by the Lamina cribosa, an 

 anterior and a porterior part. Also in the adult skull these three 

 parts are visible in spite of the pneumatising. Comparison now shows 

 that the lengthening of the septum is almost entirely brought about 

 by the increase in length of that part of it which lies before the 

 lamina cribrosa. One has only to compare the dotted lines in the 

 two figures, indicating the plane through the anterior edge of the 

 Lamina cribrosa. These lines are also serviceable for gaining an 

 insight into the forward shifting, resulting from this mode of growth. 

 In the small young skull almost the whole of the orbital cavity 

 lies behind this line, in the adult skull only the posterior part. 



Thus the growth of the skull of Gorilla has an evident influence 

 on the position of the orbits with regard to the cranial cavity. That 

 this is accompanied by a considerable change in the shape of the 

 orbital cavity, is also perceived by comparing figure 1 and 2. In 

 the adult skull the posterior part of the orbit has been drawn out 

 in the shape of a funnel or canal. 



The change of position of the orbit caused by growth can be 

 illustrated in a simple manner by projecting the outlines of this 

 cavity on the median plane, which is easily done by means of the 

 well-known Martin pantograph. Fig. 4 shows such a [)rojection taken 

 from the skull of a Gorilla child in which the tooth-change had 

 commenced (the medial incisors have been changed; fig. 5 a similar 

 projecticm of the skull of an adult man ^). The cranial base is partly, the 



1) Fig. 5 is on a smaller scale tlian fig. 4. 



