THE SKELETON IN THE FLYING LEMURS. 189 



The postacetabular poi'tiou of the pelvis is triangular iu outline, the 

 acetabulum occupying one angle, the syinphysis pubis another, and the 

 remaining one being at the tuberosity of the ischium, the last two being 

 rounded off. Upon its mesial aspect this part of the bone is uniformly 

 and moderately concave throughout, and entirely unmarked by elevations 

 or depressions. It encloses the very large, oval, obturator foramen, the 

 larger end of vrhich is formed by the isehiopubic rami, where its margin 

 is sharp and clean cut, it being thicker and more rounded for the 

 remainder of the curve of this vacuity. 



Externally the surface of the postacetabular part of the pelvis is like- 

 wise smooth, with its convexity corresponding to the concavity of the 

 mesial aspect. But one muscular line marks it, and that the usual one, 

 halfway between the obtui-ator foramen and the tuberosity of the ischium, 

 indicating the limitations of the areas where arise certain important 

 muscles of the thigh, or more exactly, of the posterior femoral and 

 adjacent regions. 



The external borders bounding this postacetabular portion of the 

 pelvis are rounded, smooth, and continuous for the pectineal line, con- 

 tinuous and slightly thickened for the ramal line, and considerably 

 thickened where formed dorsally by the ischium. The ischium presents 

 two prominent tubercles just without the rami of the cotyloid cavity; 

 They ai'e separated by a shallow valley or notch, and the anterior one 

 has generally been designated as the "spine of the ischium," at least, it 

 has been so-called in the human skeleton, where it affords surface for the 

 origin of the gemellus superior muscle, the gemellus inferior arising 

 from the other tuberosity. These muscles among the lower mammalia 

 are generally known as the gemellus anterior and gemellus posterior, 

 owing to the direction of the longitudinal axis of the body. 



THE SICKLETON OF THE PECTOBAL LtMB. 



Both pairs of limbs in Cynocephaliis are fully and powerfully devel- 

 oped, and they present many points of considerable interest. In writing 

 upon the subject of "the adaptive changes which take place in the seg- 

 ments of the limbs proper in various animals," Flower ^^ has said ; 



In what may be considered the first stage of modification each segment of the 

 limb is simply bent upon the one above it. The proximal segments (humerus 

 and femur) remain unchanged in position, the dorsal surface still looking upwards, 

 and the ventral surface downwards, the middle segment is bent do%vnwards, so that 

 its ventral surface faces inwards and its dorsal surface outwards; and 'the 

 joints between these segments (elbow and knee) form prominent angular pro- 

 jections^ 



The third segment being bent to a greater or less degree, in the opposite direc- 

 tion to the middle one, retains much of its primitive position, the dorsal surface 

 being directed upwards and the ends of the digits pointing outwards. The rela- 

 tions of the pre-axial and post-axial borders of the limb are unchanged. No 



"Osteology of the Mammalia (1885), 365, 366. 



