520 ANATOMY OF VERTEBRATES. 



caudal vertebrae. Seven pairs of ribs directly articulate mth the 

 sternum, which consists of six bones, slender as in all previous 

 Quadrumaria. 



In the Gibbons, with D 13, the lumbar vertebrae are 5, save in 

 Htjlohates syndactylus, fig. 189, where they are reduced to 4. In 

 the Silvery Gibbon {H. leuciscus), the transverse process of the 

 atlas is only perforated lengthwise and the neural arch grooved 

 by the vertebral artery. A pleurapophysial part of the trans- 

 verse process begins to project forward on the fifth cervical, and 

 becomes a distinct and larger depressed plate on the sixth : the 

 transverse process of the seventh is a simple diapophysis, and is 

 imperforate. The metapophysis and anapophysis become distinct 

 in the twelfth dorsal, and diverge from each other with increase 

 of size in the thirteenth. The anapophysis disappears in the 

 lumbar vertebrae, whilst the diapophysis reappears and the met- 

 apophysis is retained. The interlocking joints, common to the 

 preceding Quadrumana with Carnivora, here and henceforth 

 cease. Seven pairs of ribs directly join the sternum, which con- 

 sists of the manubrium, the body, which consists of two or more 

 anchylosed broad and flat bones, and a slender bony base of the 

 * ensiform cartilage.' Two pairs of ribs, and part of a third pair, 

 articulate with the manubrium. 



In the Siamang (//. syndactylus, fig. 189), the last dorsal shows 

 well the separate diapophyses, metapophyses, anapophyses, and 

 zygapophyses, more particularly the distinction between the an- 

 terior zygapophysis and the now superadded metapophysis. The 

 diapophyses are broad depressed plates, progressively increasing 

 in the first three lumbar, whilst the anapophyses diminish and 

 disappear on the third lumbar. The metapophysis recedes from 

 the anterior zygapophysis in the last lumbar, and becomes quite 

 distinct from it in the first sacral, in which, nevertheless, the ar- 

 ticular surface of the zygapophysis has a nearly vertical position. 

 The sacrum, by its greater breadth and the number of vertebrae 

 forming it, indicates the nearer affinity of the Siamang, than of 

 other Gibbons, to the Orangs. 



In the Orang-utan (Fithecus Satyrus), the vertebral formula 

 is: — 7 cervical, 12 dorsal, 4 or 5 lumbar, 5 or 6 sacral, 2 or 3 

 caudal. The transverse process of the atlas is bituberculate, and 

 is perforated lengthwise by the vertebral artery, which afterwards 

 grooves the neural arch : there is a low hypapophysial tubercle, 

 but no neural spine. The transverse process of the axis is deeply 

 grooved, but not perforated ; consisting almost entirely of the 

 pleurapophysial portion. In the third vertebra the two portions 



