146 COUES ON THE OSTEOLOGY 



it joins again about an inch from its origin, — leaving a space filled up only by membrane 

 This may very possibly be regarded as the rudiment of an eleventh rib, of which the 

 vertebral portion is wholly wanting. It is sometimes entirely obsolete. 



The latter ribs project so far backwards, that the thoracic parietes are prolonged some 

 distance behind the acetabula, and consequently the femur in its normal position lies 

 directly over the last three or four ribs, and moves backwards and forwards upon them 

 The angle of the last rib reaches within less than two inches of the posterior extremity of 

 the elongated obturator foramen. 



Sternum. This bone is sub-rectangular in shape, longer than broad, the greatest length 

 being to the average width as two to one. The length in a direct line from the manubrium 

 to the tip of the xiphoid cartilage is 7.25 inches; width opposite the superior angles, 3.25 • 

 width at narrowest part (which is opposite the facet for the sixth rib), 3.00 ; at widest part 

 (opposite the middle of the apophyses), 3.75. Length of keel along its curved edge, 8.40 

 The anterior border is sinuate, projecting at the central line, running backwards as far as 

 the groove for the coracoid bones extends, then turning forwards and outwards to the 

 anterior angle of the bone. Directly on the median line lies the manubrium, in this genus 

 extremely small, merely a slight triangular elevation of bone. The facets for the articu- 

 lation of the coracoids are very deep sulci, meeting each other on the median fine, and 

 extending outwards for two thirds of the width of the bone. The edge of the sternum is 

 thick and strong as far as these grooves extend ; externally to them it is merely a thin plane 

 bone supporting the costal facets, forming what are called the "costal processes." 



The lateral edge of the sternum measures five inches in length. It is sinuate as regards 

 both a vertical and horizontal plane. It is at first deeply concave, the edge introcedino- 

 towards the central line; but it bulges out again opposite the base of the lateral apophyses 

 and then curves again somewhat towards the central line, producing a convex outline 

 This margin is quite thick anteriorly, but becomes posteriorly exceedingly thin and atten- 

 uated. It is marked with articular facets for the sternal ribs ; these facets being closely 

 aggregated together anteriorly, becoming much further from each other posteriorly till 

 they cease opposite the base of the lateral apophysis. 



The posterior margin is a peculiar one j this arising from the great length and width of the 

 xiphoid appendage, and the depth of the lateral excavations. Considerino- the posterior 

 margin as beginning with the tips of the lateral apophyses, there is immediately a We 

 elliptical excavation an inch and a quarter deep by nearly an inch broad. Across this Is 

 stretched the ordinary dense semi-transparent membrane. Just at the postero-internal 

 border of this excavation there is another notch, but only a very slight one scarcely a 

 tenth of an inch in depth or width. From the edge of this second notch, the posterior 

 border of the sternum on each side is regularly convex, meeting on the median line by a 

 rounded but somewhat acute angle. This xiphoid appendage is very thin, and curls up- 

 wards and backwards from the plane of the sternum. 



Posteriorly, the surface of the sternum is very broad and flat, or even slightly concave- 

 anteriorly, it is narrower, and exceedingly concavo convex, the sides rising upwards from 

 the central portion which is thus caused to bulge downwards, with a very convex surface 

 The superior surface of the bone is quite smooth and free from inequalities ; the inferior 

 surface is marked with various ridges and roughened portions, indicative of the extent of 

 origin of the several pectoral muscles. The most conspicuous of these is a ridge running 

 obliquely backwards and inwards from the outer angle of the coracoid facet. 



