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morphological landmark, and that it always indicates the boundary between 

 the neurapophysis on the one hand, and the diaphysis or osseous centrum 

 on the other j so that any process which is given off from the vertebra 

 above the suture, is supposed to arise from the neurapophysis, while those 

 given off below it only, are said to arise from the centrum. 



It is only necessary to cite a few facts, which may be readily verified, 

 however, to show that the neurocentral suture is of no value as a test of 

 the nature of the parts above and below it. 



In man and in the pig, the heads of the ribs, whether dorsal or cervical, 

 are (as Retzius has well pointed out) articulated above the neurocentral 

 suture ; and therefore, if we accept the ordinary definition, not to the 

 centrum at all, but to the neurapophysis. Furthermore, if we accept the 

 ordinary view, the " inferior transverse processes " in the neck of these 

 animals are not parapophyses, but second diapophyses, inasmuch as they 

 arise from the neurapophyses, and not from the centrum. 



The " transverse processes " of the lumbar vertebrae are usually given 

 off above the neurocentral suture, and are therefore called " diapophyses." 

 In a young Dugong, in the Museum of the Royal College of Surgeons, I 

 find that, in the two hinder lumbar vertebrae, these transverse processes 

 are given off below the neurocentral suture. 



In iheEchidna the head of every rib is attached to the centrum, or below 

 the neurocentral suture ; and in the neck, this suture lies between the 

 upper and lower transverse processes. 



Thus, if we follow out logically the view that the neurocentral suture 

 indicates the boundary between the neurapophyses and the centrum, and 

 if we accept the current definition of diapophyses and parapophyses, we 

 arrive at the conclusion, that, in the cervical region, man and the pig have 

 vertebrae with two diapophyses and no parapophysis, while the monotreme 

 has a parapophysis and a diapophysis on each side ; that, in the dorsal re- 

 gion, the ribs in man and the pig are connected only with the neurapo- 

 physes, while in the monotreme they articulate only with the centra ; that 

 the transverse processes of the anterior lumbar vertebrae of the dugong 

 are diapophyses, while those of the posterior ones are parapophyses ! 



The crocodile and some extinct reptiles, such as the Ichthyosaurus, 

 whose ribs are throughout attached to the centra, afford still more striking 

 instances of the confusion which would be produced by taking the neuro- 

 central suture as a morphological boundary. 



Muller has argued that it is a distinctive character of fishes to have the 

 ribs attached to the centra of the vertebrae or to parapophyses, and his 

 views have been adopted by other anatomists ; but the ribs of the 

 Ichthyosaurus and of the Echidna are as completely and solely attached to 

 their centra as those of any fish ; so that if we merely take the facts 

 furnished by anatomy, the doctrine that there is anything peculiarly 

 piscine* in the attachment of the ribs to the centra only, falls to the 

 ground. 



But it may be urged that the connexion of the head of the rib with the 

 centrum, in mammals and the higher Vertebrata, is secondary, that with 

 the diapophysis being the primary and essential one. This is a very 



