6o4 



ON THE THEORY OF THE VERTEBRATE SKULL 



primary connexion of the ribs is with the diapophyses. On the other hand, they 

 teach that the ribs in the mammal are, as in the fish, primarily continuous with the 

 centre of the vertebrae — a result which is in perfect accordance with the ordinary 

 embryological relations of the higher and lower animals. 



The hffimapophysial cartilage passes off from the paraphysial cartilage on the 

 one hand, just as the neurapophysial cartilage is given off from it on the other. 



If the hremapophysial cartilage becomes divided into rib and process, at 

 some little distance from the centrum, the rib is said to be attached to a para- 

 pophysis ; and I believe that the only consistent definition that can be given 

 of a parapophysis is, that it is developed from the proximal end of a haema- 

 pophysial arch. 



riGA 



Fig. ID. — Vertebra; of an embryonic mouse |ths of an inch long. A. The penultimate dorsal 

 vertebra. B. A middle dorsal ; and C. an anterior dorsal vertebra. D. A posterior 

 cervical vertebra. N. Metaneurapophysis or neural spine. N. A. Neurapophyses. Z. 

 Zygapophysis. di. Diapophysis. P. Rib or pleurapophysis. t. Its tubercle. D. 

 Diaphysis. The ossified parts are shaded, the cartilaginous, dotted. 



If the paraphysis is merged in the general body of the vertebra, and the rib 

 becomes distinctly articulated close to it, the attachment of the rib is said to be 

 to the centrum. 



If the paraphysis is bent upwards, so as to pass insensibly in direction into 

 the neurapophysis, and becomes ossified in continuity with the latter, the head 

 of the rib is said to be attached to the neurapophysis, although, in truth, the 

 head of the rib, or at any rate the proximal end of the hsemapophysial arch 

 of which that rib is a part, always retains, so far as we have any evidence, its 

 primitive connexion with its vertebral centrum, into whatever new ones it may 

 ■enter. 



If the neurocentral suture does not define the lower limits of a neurapophysis, 

 and if the true definition of a parapophysis is that given above, it is obvious that 



