XVII.] SIRENIA. 293 



above the attachment to the sacrum. The iliac and gluteal 

 surfaces are widely expanded, especially at the upper part, 

 and, the pelvis being set nearly vertically to the vertebral 

 column, they face almost directly forwards and backwards. 

 The outer or acetabular border is short and deeply hollowed. 

 The pubic and ischial portions are comparatively small, the 

 atter being very little produced backwards beyond the 

 symphysis. 



In the SiREXiA, the pelvis is extremely rudimentary, being 

 composed, in the Dugong, of two slender, elongated bones 

 on each side, placed end to end, and commonly ankylosing 

 together. The upper one, which represents the ilium, is 

 connected by a ligament with the end of the transverse pro- 

 cess of the sacral vertebra ; the lower one is the ischium, 

 or ischium and pubis combined, and approaches, though it 

 does not meet, its fellow of the opposite side. 



In the adult Manati, the innominate bone is represented 

 by a single irregular triangular bone, connected by rather 

 long ligaments with the vertebral column above^ and with 

 the opposite bone across the middle line. 



There is no trace of an acetabulum, or of any portion of 

 the limb proper in any of the existing Sirenia ; but in the 

 extinct Halithcriuni an acetabular depression and rudi- 

 mentary femur have been discovered. 



In the Cetacea the pelvis is reduced to a pair of elon- 

 gated, slender bones (each of which ossifies from a single 

 centre), placed on each side of, and rather below, the ver- 

 tebral column, lying nearly parallel to its long axis (though 

 they converge somewhat anteriorly), and opposite the spot 

 where the chevron bones commence to be developed 

 beneath the bodies of the vertebris. These bones probably 

 represent the ischia, and their principal function is to 

 give attachment to the crura of the penis or clitoris, as 



