THE INNOMINATE BONE 47 



angle meets the antero-internal angle of the ischium to the inner side 

 of the obturator foramen. 



The innominate bone develops from three principal centres of 

 ossification, one for each of the three divisions. In addition to these 

 there are three supplementary centres, one for the crest of the ihum, 

 one for the cotyloid cavity, and the third for the tuber ischii. 



FRACTURE OF THE INNOMINATE BONE 



To the surgeon the innominate bone is of great importance. It is 

 one of the most common seats of fracture, and amongst the lower 

 animals fracture is most frequently met with in the horse. 



We have already pointed out, in our superficial examination, the very 

 important surface landmarks which are caused by parts of this bone, 

 and reference has been made above to the numerous muscles to which 

 it gives attachment. Quite a number of vessels and nerves bear an 

 intimate relationship to the bone, and fractures are very frequently 

 complicated by injuries to these structures. Within the pelvic cavity we 

 have the rectum, bladder and urethra, vagina (in the female), &c., and 

 these may also be injured by inward displacement of fractured pieces. 



As one would most naturally expect from its exposed position the 

 external angle of the ilium is the most common seat of fracture. 



The angle of the croup is also a common seat, as is also the tuber 

 ischii. Other parts frequently fractured are the shaft of the ilium, 

 the pubis and ischium either through or parallel to the ischio-pubic 

 symphysis, the pubis in front of the obturator foramen, the pubis 

 slightly anterior to its posterior angle, i.e., to the inner side of the 

 obturator foramen, the ischium just behind the acetabulum, i.e., behind 

 its antero-external angle, through the cotyloid cavity, &c. Two or more 

 of these fractures may occur simultaneously. 



Fracture, through the angle of the haunch, may be due to the part 

 being caught in a narrow doorway, or in young animals through their 



