The Squirrel Monkeys have a small face, and the brain-case behind it is moderately arched above, and sticks out behind very decidedly. This is because the head is placed on the spine differently to the Monkeys already described. In them the opening in the under part of the skull, for the passage of the spinal cord (the foramen magnum) is far back, but in the Squirrel Monkeys it is much further forward; so far forward, indeed, that there is enough room for brain matter behind it to allow the back part of the brain to be relatively larger than in man. Huxley remarks that in this Monkey the cerebral hemispheres (that is to say, the whole of the “brain proper”) project beyond the cerebellum to a greater relative extent than in any other Mammal nearly by one-fifth of their total length. But the fore part of the brain is small, and there are very few convolutions. On referring to the description of the Howlers, this great difference will be appreciated. Gervais, with a laudable desire to account for the great development of the back part of the head, insists on the great love the young show their mother, not leaving her even when she is dead. The orbits of this Monkey are large, and are close together; they are not perfectly separated by bone, for a membrane shuts one off from the other; and the cheek-bone has not the round hole in it which is observed in the Spiders and Howlers. As a whole, the head is very human-like, especially when it is young; but the forehead-bone is triangular, and projects upwards and backwards between the side bones of the head, and the chin is round and prominent. The forehead is narrow, and the muzzle is more protruding, however, than in man.[94]