XIII 



PHYLUM CHORDATA 



523 



suture between the premaxilla and the maxilla only becomes 

 obliterated, if at all, in old individuals. The mental prominence 

 of the mandible is never developed, the anterior surface of the 

 symphysial region sloping backwards and downwards from the 

 bases of the incisor teeth. The stylo-hyal never gives rise to an 

 ossified styloid process. 



In the skull, as in many other respects, the Lemurs occupy an. 

 intermediate position between the higher Primates and the lower 

 orders of Mammals. The occipital and ethmoidal planes are 

 usually vertical. The tympanic forms a large bulla. The orbits, 

 which are large, are usually separated from the temporal fossa 



).^ (After; Blainville. 



FIG. 110S. Skull of Chimpanzee (Aiithropopithecus 



only by a narrow rim of bone. The lacrymal foramen is situated 

 on the face outside the margin of the orbit. The facial region is 

 usually elongated, and may form a prominent muzzle. 



In all the Primates the clavicle is present and complete, and 

 in the scapula, the spine, acromion, and coracoid process are well 

 developed. In Man and the higher Apes the glenoid border of the 

 scapula is much longer than the coracoid. In the lower Monkeys, 

 on the other hand, these borders are nearly equal. The humerus is 

 comparatively long and slender; the tuberosities and ridges are 

 not, as a rule, very strongly developed. In Man and the Simiidse 

 the bone is twisted around its long axis ; in the lower forms this 

 torsion is absent. In Man and the higher Apes the foramen 

 above the inner condyle is absent ; it is present in many of the 

 American Monkeys and in most Lemurs. Characteristic of the 

 ulna of Man and the higher Apes is the small upward extension. 

 of the olecranon process. The radius and ulna are distinct in all 



