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length, which is nearly its entire extent, judging from the thinning and round- 

 ing of the broken end. Its breadth the greater part of the length is nearly 

 uniform, and at the middle is nearly 2 inches. Toward the distal end it 

 becomes slightly less wide and thinner; toward the proximal end it undergoes 

 a greater reduction in width, and becomes much thicker. 



The upper surface of the spine, represented in Fig. 10, for the most part 

 is nearly flat except toward the rounded borders. It is invested with a 

 thin layer of ossific substance of a more dense character than the compact 

 bone beneath. The surface is striated or ornamented with raised lines, which 

 are longitudinal and parallel, but on portions of the surface are somewhat 

 irregular. Some of the lines branch, and the slightly divergent branches 

 include other commencing lines. At the distal end of the spine, near the 

 anterior border, the lines break up into finer branches which curve outwardly 

 to the edge. 



The under surface of the spine (Fig. 9) is uneven. A prominent ridge, 

 commencing at its proximal extremity and occupying more than two-thirds 

 its width, extends outwardly and gradually declines to a point near the center 

 of the inferior surface. A shallow groove commences in front of the ridge, 

 widens outwardly, and extends beyond the former upon the anterior half of 

 the inferior surface of the spine. Back of the commencement of the ridge 

 there is a concave hollow, which narrows outwardly into a deep groove, and 

 this, pursuing the same course, widens and opens downward upon the posterior 

 half of the inferior surface of the spine to its distal end. 



The posterior groove for nearly half its length proximally exhibits a row 

 of irregular pits at the bottom. The upper boundary of t he groove in advance 

 of the pits is transversely striate, and beyond the position of the pits exter- 

 nally the corresponding surface presents the stria? curling outward to the 

 back edge of the spine. The bottom of the groove, external to the position 

 of the pits, continues as a shallow channel running along the middle of the 

 spine inferiorly to its distal end. 



The anterior border of the spine is convex in the length, obtuse internally, 

 •and acute externally. The posterior border is concave longitudinally, obtuse 

 internally, and less acute externally than the anterior border. 



The inner extremity of the spine appears bent upward into a hook-like 

 eminence with a pyramidal base extending above the general level of the 

 spine. The end of the hook-like process is broken off. Its inner surface 



