In the female of the _Simia morio_, which is the smallest Orang, all the structures just mentioned as characterising the young _Simia satyrus_ and the young male _Morio_ are exaggerated. There are faint frontal ridges also, and the back ridge or crest is shown, but there is hardly any difference in the size of the brain case. The front bone of the upper jaw is very distinct; and the creature whose skull is in the British Museum had its permanent teeth, the milk ones having fallen. There was the same number of teeth as in the Troglodytes and in man. But it is in the old males that the juvenile structures are greatly altered; and it is indeed hard to believe their skulls ever could have belonged to the same species. In the old males the brain case has not increased in its capacity, but it is furnished with huge ridges along the front and crossing behind. The ridges commence on the brow ridges and the outside of the orbits, which are no longer nearly circular, but flattened above; they pass on to the forehead, and curve to join in the middle line of the skull, forming a crest. This meets at the back a crest coming from the tip of each ear-bone. The cheek-bones are huge and wide apart; the upper canine teeth are great, and their sockets mark the face. The palate is huge, wide, and not arched; and the upper middle incisors project, and are very large, cutting indeed upon three of the lower ones. [Illustration: WRIST BONES OF ORANG.[17]] All the roughnesses for the attachment of muscles are great, and the lower jaw is immense, and the tooth next to the lower canine--the first false molar--is pointed and cutting behind. Finally, the opening for the spinal cord (the foramen magnum) is round in front, and the condyle joints are close to its anterior margin. These are changes during the growth which are worth considering, especially as they cause the animal to depart from many of its man-like characters, which are so well seen in the young and in the females. The Orang has no uvula, and the papillæ of the back of the tongue are in the shape of the letter V. Its stomach differs somewhat in shape from that of man and the Troglodytes, but its vegetable diet determines the existence of a large intestine which has a little ending or appendix (vermiformis) as in man. [Illustration: SIAMANG.] CHAPTER IV. THE MAN-SHAPED APES (_concluded_)--THE GIBBONS[18]--1. THE SIAMANGS--2. THE TRUE GIBBONS. General Characteristics of the Species--THE SIAMANG--Its Habits and Anatomy--Distinctness from the Orangs and Gibbons--Special Peculiarities--THE WHITE-HANDED GIBBON--Where Found--Its Cry--Its Habits--Special Anatomical Features--THE HOOLOOK--Where Found--A Young One in Captivity--Shape of the Skull--THE WOOYEN APE--Its Appearance and Habits--THE WOW-WOW--Very little Known about it--THE AGILE GIBBON--Reason of the Name--Peculiarities of the Anatomy--General Comparison of the Different Varieties of the Great Apes.