This index becomes larger as the foramen magnum lies more 
oceipitally. 
1 shall now first give the basal indices found with the skulls of 
the different apes, those of man will be given later. 
Index basalis of skulls of monkeys. 
Hapale 77, 72, 71, 70, 70, 68. Average 71 . 
Chrysothrix 62, 61, 60, 60, 60, 59, 58, 58, 57, 56. Average 59 
Cebus 71, 70, 70, 69, 68, 68, 67, 65, 64, 64. Average 67 . 
Ateles 67, 66, 65, 64, 61, 58. Average 64 . 
Pitkecia 76, 75, 74, 70. Average 74 . 
Mycetes 95, 91, 86, 84, 78. Average 86. 
Inuus 67, 65, 65, 64, 63. Average 65 . 
Cynocephalus 69, 66, 60. Average 65 . 
Macacus 69, 69, 66, 65, 65, 63, 62, 60, 60, 60. Average 64 
Cercopithecus 60, 60, 57, 54. Average 57 . 
Semnopithecus 76, 76, 74, 71, 70.- Average 74 . 
Colobus 76, 74. Average 75 . 
Siamanga (adult) 78, 77, 76, 76, 76, 75, 75, 75, 73. Average 76 . 
Siamanga (juv.) 70, 62. 
Hylobates 66, 67, 71, 72, 80. 
Chimpanse (adult) 65, 63. Average 64 . 
Chimpanse (juv.) 53, 50. 
Gorilla (adult) 67, 66, 65, 62, 59, 58, 58, 56. Average 61 . 
Gorilla (juv.) 54, 50. 
Orang (adult) 69, 65, 60, 60, 58, 58. Average 61 . 
(hang (juv.) 55, 53, 51, 51, 50. Average 52 . 
Leaving aside for the present the infantile skulls, the basal index 
appears strongly to vary with the different simian genera, while 
moreover no inconsiderable individual variations exist. The highest 
average was found with Mycetes, the lowest with Cercopithecus. At 
the same time the correctness appears of what had already been 
asserted by Huxley, that the position of the foramen magnum in 
the cranial base, does not depend on the place occupied by the genus in 
the system. This is shown most clearly, if the genera are arranged 
according to the average value, found for their basal index, beginning 
with the genus with the highest index, where the foramen magnum 
hes hindmost. The following series is obtained: Mycetes, Siamanga, 
Colobus, Pithecia, Semnopithecus, Hapale, (Hylobates), Cebus, Inuus, 
Cynocephalus, Macacus, Ateles, Chimpanse, Gorilla, Orang, Chryso¬ 
thrix, Cercopithecus. 
