FAUNA OF THE GOSATJ FORMATION". 



655 



especially are roughened with ligamentous attachments and mus- 

 cular rugosities. The thickness of the bone rapidly "diminishes 

 above the articulation ; and it continues to become thinner towards 

 the free end, where the thickness does not exceed a centimetre 

 and a half. The posterior margin is compressed and rounded, 

 the rounding becoming more conspicuous as the surface ap- 

 proaches the humeral articulation, owing to the increasing thick- 

 ness of the bone. The length of the posterior side of the bone is 

 about 25 centim. ; its outline is concave ; the concavity, as preserved, 

 may be indicated by the fact that the chord joining its two ex- 

 tremities is 21 centim. long, and the abscissa 6 centim. high. The 

 corresponding anterior margin is not quite parallel, since the bone 

 is wider in its upper third than in its lower third; and hence the 

 anterior margin is more convex. The least transverse measurement 

 above what may be termed the spine of the scapula is 6| centim. 

 In the upper third of the bone the width has increased to upwards 

 of 8 centim.; it then contracts a little to less than 8 centim., so as 

 to make the anterior termination of the superior margin concave ; 

 for the bone widens once more, so as to become broader than ever 

 at its free end. The posterior corner of the free end appears to 

 be curved a little outward. The external surface is smooth, con- 

 vex in length, and more convex in breadth at the distal end than 

 proximally. The visceral surface exhibits corresponding characters. 

 The anterior margin of the bone is thicker, better rounded than 

 the posterior margin, and rougher with muscular attachments. As 

 preserved, the measurement from acromion to the anterior distal 

 margin is 23 centim. in a straight line. In about the middle of 

 the anterior margin the bone becomes appreciably thickened on 

 the inner side with muscular attachments, and the thickness in- 

 creases until a vertical anterior shoulder is formed almost at right 

 angles to the spine of the scapula, extending downward and inward 

 towards the coracoid area. Only a small portion of this trian- 

 gular space is preserved ; but so much of it as is seen below the 

 acromion is 4 centim. deep. The spine of the scapula only runs for 

 a short distance along the proximal part of its surface, and is diffi- 

 cult to define, because the bone is obviously compressed so as to 

 make the surface posterior to the spine appear more concave than 

 it really was ; but the spine may be considered to originate in 

 the thickening of the anterior margin of the bone already alluded 

 to ; and it becomes most distinct a centimetre or two above the 

 acromion, where it is 1^ centim. wide, flat above, and margined at 

 the sides by rounded ridges. It is prolonged into a free process or 

 acromion, which was directed forward and outward. This process is 

 a little crushed, is nearly 5 centim. long, 33 millim. broad, and, as 

 preserved, about 2 centim. thick, though before crushing it was 

 thicker ; the corners and angles of its free end are rounded ; and 

 the inferior or internal surface is concave, since it rises from the 

 anterior coracoid border of the bone. The plane of the acromion is 

 parallel to that of the blade of the scapula, and makes an angle of 45° 

 with the direction of the humeral articular surface. The distance 



