10 EINAR LONNBERG, MAMMALS COLLECTED IN CENTRAL ATRICA. 



but probably, when the time comes, develop rather suddenly. As pointed out above 

 the skin of the semiadult male n:o 165 shows no sign of the particular colour of the adult 

 male, although the animal is so old that the third molars of the lower jaw are fully deve- 

 loped, and in the upper jaw m" is up on the right side, but cutting the gum on the left. 

 In a similar way the skull n:o 165 lacks many features of the adult. The eyebrow ridges 

 (PI. IV, fig. 1) are not thicker than those of the adult female, and the orbital walls gener- 

 ally are much less thick than in the old male. The crests, which are so very characteristic 

 for the skull of the adult male Gorilla, are entirely lacking in the semiadult (PI. Ill, fig. 2). 

 The development of the musculature of the jaws has not reached further than that a 

 broad median space on top of the skull is left free (PI. IV, fig. 1). At sutura coronalis 

 (which still is open) for instance the distance between the lineas of insertion for musculi 

 temporales is 23,5 mm. broad. The absence of the crests causes that the planum Tmchale 

 has not yet received its definite shape and size. Lamince pterygoidece are not yet deve- 

 loped as in the adult which also stands in correspondence with the juvenile stage of the 

 musculature. For the same reason the breadth of ramus adscendens of the lower jaw is 

 only 64 mm. against 80 mm. in the old male, and ramus horizontalis below m^ is only 34 

 mm. in the former, against 43,s mm. in the latter, and so on. Other differences in the 

 dimensions are expressed in the table of measurements. 



The brain -case of these Gorillas appears to attain its definite size, or at least its 

 width at a comparatively early period as this measurement is almost as great in the young 

 animals as in the old, especially if it is taken into account that the walls are thickened 

 with age. The anterior portion of the skull grows more than the posterior, and the postor- 

 bital constriction becomes more pronounced with age, which stands in connection with 

 the much increasing musculature of the jaws which needs more and more space. During 

 this development the frontal grows forward. In the yongest male skull (n:o 166, PI. IV, 

 figs 2 & 3) the distance between sutura coronalis and the front of the eyebrow-ridge 

 measures in the median line 67,5 mm., in the skull n:o 40 the same measurement is 75,5 

 mm., and in the semiadult (n:o 165) 88 mm. The above mentioned increase of the postor- 

 bital constriction with age in connection with the growth of the musculature of the jaws 

 is quite analogous to the corresponding proceedings in the development of the skulls 

 of f . i. baboons and carnivorous animals. The very long and narrow palate of these Goril- 

 las, more than in other species, (PI. II, fig. 2) also remind strongly about the same 

 parts of Baboons, so that there might be spoken about a certain analogy in the deve- 

 lopment of the jaws of these animals. In a young Baboon^ with milk -dentition the 

 length of the palate is less than a third of the length of the skull, in a somewhat older 

 animal with the first molar developed the length of the palate is contained 2 7^ times in 

 the length of the skull, and in the adult the same relation is 2 V^ times. In the young 

 Gorilla (n:o 166) with only first molar developed the length of the palate is contained 

 about 2 7^ times in the length of the skull, in the male with the second molar developed 

 (n:o 40) about 2V3 times, and in the old one (n:o 164) not quite 2 7^ times. These re- 

 lations are thus pretty similar. If the length of the palate of these Gorillas is com- 

 pared with the condylobasal length the former measurement is found to be 51 % of the 



1 Papio tessellatus cf. below. 



