v 1 ///-: ro?<Ti-:i;nii: /./.u/;- .>:, 



ft inns, with that of the other ischhnn, the summit of the triangular space 

 which constitutes the ischiatic arch, or pubic arch of some species. 



Tin: COXA IN GENERAL. The bone whoso three constituent parts we have 

 jn-4 l>oen studying, presents for consideration, as a whole, a middle portion 

 and two extremities. The middle, very much contracted, offers, outwards 

 and downwards, the colyloid cavity (or acetabulum), which has not yet been 

 described, because its study does not properly pertain to either of the three 

 n u'ions of the coxa. This cavity is intended to receive the articulating head 

 of the femur, and represents the segment of a hollow sphere ; it is circum- 

 scribed by a very salient rim which is thin at its free margin and widely 

 notched on the inner side. The deeper portion is occupied by the rough- 

 ened und depressed surface already designated as the bottom of the cotyloid 

 cavity (//<<///* nct'tabuli), and which communicates by the internal notch of 

 the rim with the inferior groove of the pubis. The anterior extremity, 

 flattened on both sides, and formed by the ilium, rests, as has been shown, 

 on the sacrum. The posterior extremity, flattened in an inverse sense to the 

 preceding, is constituted by the pubis and the ischium, and traversed, from 

 above to below, by the sub-pubic (or obturator} foramen, the large oval 

 aperture which separates these two bones from one another, and perforates 

 the floor of the pelvis ; this opening is closed in the fresh state by muscles. 



The two COXSB, by uniting in their posterior part, form the articulation 

 to which has been given the name of ischio-pubic or pelvic symphysis ; thus 

 united, the two bones represent something like a V with the opening in 

 front ; a circumstance which makes the lateral diameter of the pelvis greater 

 in front than behind. 



STRUCTURE AND DEVELOPMENT OF THE COXA. To the three centres of 

 ossification which constitute the coxa, are added two complementary 

 centres : one for the anterior spinous process and spine of the ilium, another 

 for the ischiatic tuberosity. 



In youth, the different parts of the coxa are very thick, and the spongy 

 tissue is abundant, while the compact is rare. The pubis is always convex 

 on its two faces, and the middle part of the coxa that adjoining the cotyloid 

 cavity is of considerable thickness, a feature which much diminishes the 

 extent of the pelvic reservoir. As the animal advances in age, however, 

 the layers of compact tissue increase in thickness, approaching each 

 other as the spongy substance is lessened. The pubis becomes thinnest, and 

 ;it an advanced period of life is sometimes even translucid. 



The compact tissue is always abundant in the neighbourhood of the 

 cotyloid cavity, as this is the centre on which converge all the impulsive 

 efforts communicated to the trunk by the posterior limbs. It is also in this 

 cavity that ossification commences. 



B. The Pelvis in General. 



1. EXTERNAL AND INTERNAL CONFORMATION cr THE PELVIS. The pelvis is a 

 kind of rear cavity in the form of a cone, which prolongs the abdominal cavity. 



It occupies the posterior part of the trunk, and with regard to its 

 conformation, presents for study an external and an internal surface. 



External surface. This may bo resolved into four regions or faces. 



The superior region is slightly oblique from alxtve to In-low, ami l>cforo 

 to lx:hiii'l: its decree- of obliquity varies. It is contracted from U fore to 

 )< hind, and shows: 1, On the median lino, the spinous processes of the 

 sacral and the first cocnygeal vertebra ; 2, On each side the sacral grooves, 

 at tin- bottom of which open the supcrsacral canals. 



