108 ESCHRICHT AND REINHARDT 



able in an outward direction towards both sides, and in its entire transverse course between 



the sixth and the seventh ; between the most 

 posterior cervical vertebra (7 in the woodcut) 

 and the foremost dorsal one an ankylosis also 

 sometimes takes place. The inferior transverse 

 processes are only partially ankylosed, and in 

 different ways, frequently not at all. 



In the lateral surfaces (see the woodcut 

 in the preceding page) the bodies of the two 

 foremost vertebræ appear to be so completely 

 ankylosed that here, as in the ventral surface, 

 not even the limits between them can be dis- 

 tinguished, while in all the succeeding vertebræ 

 these are indicated by deep transverse grooves. The same is also the case with the superior 

 surface (that which forms the floor of the spinal canal) of these vertebræ. 



On the dorsal surface of the osseous block formed by these eight ankylosed vertebræ, the 

 ankyloses will be observed to be most complete along the mesial line of the arches, where all the 

 foremost six vertebræ form one continuous ridge, with the exception that this ridge in the speci- 

 men before us is interrupted between the fourth and fifth, in other cases between the fifth and 

 sixth vertebræ. At either side of this osseous ridge the atlas and the axis appear completely 

 separated when seen from this (the dorsal) side, and the same is the case with the sixth and 

 seventh vertebræ. 



The arches of the third, fourth, fifth, and sixth vertebræ, as well as the superior transverse 

 processes issuing from them, are irregularly ankylosed, and these processes partially rudimentary. 

 Thus, as not only nearly all the inferior processes of the cervical vertebræ, but also the superior 

 ones of the greater part of these vertebræ are only rudimentary, the wide-gaping but very short 

 canalis intervertebralis (see the woodcut, page 107, and Plate II, fig. 3), is of course only 

 very imperfectly surrounded. The broad lateral parts of the atlas project as a wall before it 

 (Plate II, fig. 3, 1'). The blood hi that arterial rete mirabile, which represents the vertebral 

 artery, is observed to find its way into a large trunk, the deep groove for which is placed on the 

 dorsal surface between the atlas and the axis. Parallel with this another deep arterial groove, 

 sometimes partially changed by means of an osseous bridge into a short tube, runs on the 

 anterior surface of the atlas. 



The spinal canal, formed by the dorsal surface of the bodies of the vertebræ and the vertebral 

 arches, is in its most anterior part almost circular in circumference, six inches in diameter, but 

 posteriorly its breadth (eight and a half inches) becomes much greater than its height (five and a 

 half inches). When the ossification is complete, there is no other communication between it and 

 the cavities for the arteria intervertebralis than through the intervals between the inferior half of 

 the arches (that between the body of the vertebra and the superior transverse processes), but very 

 frequently this half of the arch is either not at all or only partially ossified, either in the third 

 vertebra alone or in the fourth, fifth, and sixth, and in macerated skeletons the spinal canal 

 becomes thus, as it were, united into one with the two lateral canals, and the arches in question 

 are seen hanging over the canal in the form of a bridge suspended in position only by their 

 ankylosis with the arches of the vertebræ placed before and behind. 



