454 



widely current doctrine, and it is sanctioned by Rathke, as we have seen 

 in the passages quoted above, though they are not quite consistent with 

 one another. It is with great hesitation that I venture to contravene the 

 distinct statements of so eminent and accurate an embryologist as Rathke, 

 but my own observations lead me to precisely the opposite conclusions. 



In the spinal column of embryos of the mouse 7-8ths of an inch long, 

 for instance, I find that the posterior dorsal vertebrae (A. fig. 10) have no 

 diapophyses, and that the ribs have no tubercles, but that their heads pass 

 directly into the cartilaginous substance of the centrum. Further forwards 

 (B, C) both diapophysis and tubercle become more and more developed, 

 until at length they come into contact and articulate in the ordinary 

 way. Finally, in the cervical region (D) the rib and the diapophysis are, 

 even in this early stage, confluent. 



Fig. 10. Vertebrae of an embryonic mouse fths 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. 



These facts are, I conceive, wholly at variance with the supposition 

 that the 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 centra of the vertebrae a result which is 

 in perfect accordance with the ordinary embryological relations of the 

 higher and lower animals. 



The hsemapophysial cartilage passes off from the paraphysial cartilage 



