428 



cartilage into osseous or other tissue, and thus the semi-arc becomes 

 separated into a rib and an articular surface or process, for the head 

 of that rib, to which last the term Parapophysis may be conveniently 

 restricted. 



In the dorsal vertebrae of many Vertebrata, the neural semi-arc 

 sends out a process, the Diapophysis, which is eventually met by a 

 corresponding outgrowth of the rib, its so-called tubercle, and the 

 two become firmly connected together. 



"When ossification occurs, it is a very general, if not invariable rule, 

 that an annular deposit around the notochord takes place in the 

 centrum. I term this the Diaphysis of the vertebra. In some 

 fishes a distinct centre of ossification appears in each paraphysial 

 region, and this may be termed the Paraphysis of the vertebra. 



In mammals each end of the vertebra ossifies from a distinct 

 point, and constitutes a central Epiphysis of the vertebra ; and in 

 many Vertebrata a part of the under surface of a centrum ossifies 

 separately as a distinct Hypophysis. It is another very general, if not 

 invariable rule, that a distinct centre of ossification appears in, or 

 on, eachjneural semi-arc or Neurapophysis, and passes upwards, into 

 the spine or Metaneurapophysis; downwards, to unite sooner or later 

 with the diaphysis, or diaphysis and paraphysis ; and outwards into 

 the diapophysis. 



It is doubtful whether the paraphysis appears as a distinct osseous 

 element in any Vertebrata above the class of fishes, in very few of 

 which even, is it distinguishable in the adult state. Consequently 

 in the higher Fertebrata the paraphysial region is ossified, either from 

 the diaphysis or from the neurapophysis, or from both ; and a suture 

 exists for a longer or shorter time at the point of junction of the 

 neural and central ossifications. I will term this the Neurocentral 

 suture. Its position is no certain or constant indication of the 

 nature of the parts above or below it, for it may vary in the same ver- 

 tebral column from the base of the neurapophysis, to the junction 

 of the paraphysial with the diaphysial region of the centrum. 



The number of the centres of ossification in each distal portion of 



the hsemal semi-arc may vary greatly ; the uppermost is called a 



Pleurapophysis, the lower, Hcemapophyses and Met-htzmapophyses, 



Besides these primary centres of ossification of a vertebra, there 



are others of less constancy. Thus the ends of the metaneurapo- 



