HAPLODONTID^E— VERTEBRA OF HAPLODON RUFUS. 571 



sacrum presents the usual sinuate S-shape; but the arch of the back and hips 

 is a long, gradual convexity, while the reverse convexity of the fore part of 

 the column, from about the midway dorsal point to the head, is abrupt and 

 strong, the column sinking deeply between (he shoulders and then rising 

 almost perpendicularly, as if the animal habitually carried its head thrown up. 

 This great dip of the anterior dorsal and posterior cervical vertebrae, how- 

 ever, is not visible in Ihe external contour of the animal, owing to the bulk 

 of the cervical muscles, which completely fill up the depression between the 

 shoulders and the occiput. The several divisions of the spinal column are 

 well marked by various easily recognized characters. 



The cervical vertebrae are seven in number, as usual in Mammals; of 

 these, only the intermediate three are quite similar to each other, the first two 

 and the last two having each their peculiar features. The centra of the 3d 

 to 7th vertebra? are equally short, much shorter than the body of the 2d 

 (axis) ; they increase regularly from 3d to 6th, the 7th being abruptly nar- 

 rower (about as broad as the 4th); they are all strongly flattened underneath. 

 The spinous processes of the 3d to 6th are simple, and regularly graduated in 

 length, decreasing from before backward ; the spine of the 7th is abruptly 

 longer, and more like one of the dorsal spines ; all these cervical spines are 

 much slenderer, and all but the 7th are much shorter than the great stout nod- 

 ular and ridged spinous process of the 2d (axis). The "oblique" articular 

 processes (zygapophyses) of all the cervical vertebras, excepting the atlas, are 

 substantially alike. The "transverse" (here supposed to be conjoined di- and 

 pleur-apophyses) processes of the axis and four succeeding (2d to 6th) ver- 

 tebras are substantially alike, being slender, horizontal, backwardly-projecting, 

 their two roots enclosing the vertebrarterial canal; but the last such process, 

 on the 6th bone, is transverse instead of oblique to the axis of the column, 

 and moreover develops from the under side of its root a special process pro- 

 jecting obliquely downward and backward, no trace of which is seen on any 

 other vertebra. The atlas is a simple ring of ordinary characters ; slenderest 

 in front, in the position of the centrum of other vertebrae; deeply impressed 

 anteriorly with the articular facets for the occipital condyles, bearing on the 

 other side the flatter but more prominent and more strongly margined facets 

 for the axis; the impression of the odontoid process of the latter upon the 

 middle of the ring is scarcely perceptible. A slight eminence upon the back 

 of the ring stands in place of the spinous processes of the other cervicals. 



