THE PELVIC CANAL 47 



zontal plane an angle of 45°. The pelvis, therefore, lies 

 much higher posteriorly than anteriorly. The lateral planes 

 are formed by the internal surface of the .sacro-sciatic liga- 

 ments, the internal face of the internal angles of the iliac, the 

 internal face of branches of the pubes and ischia. A part of 

 the latter also forms the floor. 



The lateral planes being partly formed by bones and 

 partly by the pelvic ligaments, they can only expand superiorly. 

 From an obstetrical point of view, the pelvic inlet is of the 

 greatest importance, as the position during labor of the calf 

 must accommodate itself to the shape of this inlet by rotating 

 around its long axis. 



The connection between the ossa innominata and the 

 vertebral column takes place by means of the sacro-iliac 

 articulation. It is formed by the wings of the sacrum and the 

 internal face of the ilium. The joint permits of but limited 

 movement ; only during the latter stage of pregnancy, when 

 the pelvic ligaments infiltrate and thus become more elastic, 

 can we speak of any movement (Franck). From an obstetrical 

 standpoint, this joint is very important. In such labor cases 

 where a great deal of power is employed to extract the calf, 

 an injury to this joint is often the cause of post-par turn 

 paralysis. The wide pelvic ligaments also unite the sacrum 

 and the coxse. The union of the innominate bones takes place 

 at the pelvic symphysis (symphysis pelvis). The union is 

 formed by cartilage, strengthened superiorly and inferiorly by 

 short connective tissue and elastic fibres, the lig. arcuatum, 

 which runs obliquely across from one pubis to the ischium, 

 uniting with the cartilage and periosteum. In young animals 

 this union is rather elastic and some little expansions possible, 

 but not after the second year. In older animals this symphysis 

 ossifies completely, and the middle portion of the pubis and 

 ischium, especially round the oval foramen, becomes thinner. 



PELVIC DIMENSIONS. 



Pelvic diameters of the domestic animal, especially the 

 horse and cow, have been established same as in man ; provided 



