598 ON THE THEORY OF THE VERTEBRATE SKULL 



neural canal, and, eventually uniting with its fellow, forms the neural arch. The 

 lower outer branch extends into the ventral wall and becomes the rib." 



The ring grows both externally and internally, so as to constrict the notochord! 

 (which softens and acquires a grumous consistence), and then becomes converted 

 into bone, so that the notochord is surrounded by a series of bony rings. The 

 notochord takes no part in the formation of the articular intervertebral surface, 

 which is an apophysis and not an epiphysis ; the neural arches ossify much later 

 than the centrum, from a single point in the middle of each. The inferior pro- 

 cesses are outgrowths of the substance of the vertebra, and in the caudal region 

 are, from the first, double. 



" On each side of the body of the vertebra, where the ribs and the vertebral 

 arches radiate from it, the condensed blastema of which it originally consists, 

 grows out slowly, but considerably, and becomes developed (gradually undergoing 

 chondrification) into a plate, whose largest surfaces are vertical, which increases 

 more in length than in breadth and thickness, and which gradually drives the rib 

 and vertebral arch further away from the axis of the vertebral column. At the 

 end of this period it is almost as thick as the length of the vertebra; ; it then 

 appears, when viewed from in front or behind, as a short irregular oblong, one 

 of whose angles psases into the body of the vertebra, and one of whose shorter 

 sides is turned outwards and upwards. From this side passes one crus of the 

 vertebral arch, while from the side which is turned outwards and downwards, 

 at least in most of the vertebras, a rib is developed, so that these processes are con- 

 nected with the originally e.xisting part of the body of the vertebra, only mediately, 

 by the plate in question. 



" The crura of the vertebral arch ossify from their middle towards both ends, 

 the process commencing very soon after the ossification of the centra ; but after 

 ossification has begun in them, these originally filiform parts widen into broad 

 oblong plates, which, in the greater part of the body, come into contact only 

 towards the end of the period, and in the tail and hindermost part of the body, only 

 in the following period. 



" The ribs ossify far later, and also from the middle towards the end. Before, 

 however, an ossific centre is developed in them, the cartilage, of which the rib now 

 for the most part consists, becomes articulated with the rest of the vertebra. The 

 plate, lastly,' which forms the union between a rib, a vertebral arch and a vertebral 

 body, and subsequently forms a part of the body of the vertebra, ossifies only in 

 the following period. 



"The relation of the ribs to the bodies of the vertebras, therefore, is originally 

 just the same as that of the crura of the vertebral arches to them : just as one of 

 these crura, does each rib arise as an outward growth of that vertebral body 

 which is the first formed of all these parts ; whilst, however, the crura of the 

 vertebral arches are directed upwards in order to enclose the spinal cord, 

 the ribs grow downwards to enclose the viscera of organic life, and in this 

 way their greater length in the snake, and a multitude of other Vertebra/a, is 

 explicable. 



" The transverse processes of the caudal vertebras e.xhibit the same relations to 

 the bodies of the vertebra;, as the ribs in the dorsal region. They arise in the 

 same places as these ; become, in like manner, removed, together with the crura 

 of the arches, by lateral outgrowths of the body from its axis ; and, before the ribs 

 are articulated, they pass quite imperceptibly into the processes in question. The 

 transition is the more remarkable, as in the snake the hindermost rib is split, in 



1 Paraphysial cartilage. 



