220 



DESCRIPTION OF A SPECBIEN 



bears a small projecting epipliysis which gives a peculiar finish to the spinal column. The 

 adjacent epiphyses of this vertebra and the preceding one, are grown into one plate about 

 3-8 of an inch thick, which is nearly smooth on its posterior aspect, but on its anterior pre- 

 sents a central spine which fits into a depression in the 25th. 



The Chevron Bones. 



These constitute the only part of the skeleton which is not in a satisfactory condition. 

 At the time of the dissection they were so soft that some were cut completely in two by 

 the workmen before they were thought of. There are parts of sixteen bones, but one 

 lateral half of the first and last are wanting, and some others are more or less mutilated so 

 that the correctness of the arrangement which has been adopted is not quite certain. The 

 two sides of the 1st, 15th and 16th had not yet united. The 1st is a thin plate slightly 

 convex on its outer side with an articular surface on the upper end ; the inferior end 

 is drawn out backward. The articular surface of the 2d and 3d is also single, after 

 which this surface is divided into two by a transverse ridge till the 11th. The bases 

 become wider transversely in proportion to the size of the bones as we pass backward. 

 The plate foi'ming the arch is constricted at the upper part in the anterior ones (except 

 the first), but becomes broad after the first few. The lower end projects both forward and 

 backward, chiefly in the latter direction. I have not been able to find any regular propor- 

 tion between the size and the position of these bones. 



The following table shows the greatest vertical and longitudinal (from before backward) 

 diameters in inches. 



Those marked with stars have a httle wanting. About a thii'd part of the 10th is wanting. 



One peculiarity in the formation of these bones deserves particular notice. They are 

 formed in two lateral pieces which appear to have been put together unevenly, that is one 

 a little in front of the other ; thus the anterior edge of one plate is continued directly on 

 the anterior edge of the spine formed by the union of the two, while the front edge of the 

 other falls a little back of it ; on the other hand, the posterior edge of the second projects 

 behind that of the first. This appearance is present in all the bones excepting two, both 

 of which are imperfect at important points. The plate on the left side is (with one excep- 

 tion) the anterior one. In most of the larger ones the keel, instead of being in the median 

 line, is somewhat deflected to the right, and the left side of the bone shows a slight concav- 

 ity suggestive of the depression which would be caused by a large artery. . 



The Ribs. 



The following descriptions and measurements are taken from the ribs of the left side ; 

 those of the right present some curious pathological alterations and will be considered 

 later. 



There are fifteen pairs of ribs articulated by their tubercles to the ends of the trans- 

 verse processes of the dorsal vertebras. The head and neck are well developed only in the 



