448 Zoological Society. 



Arriving thus at the demonstration, that the hsemal arches in the 

 tails of the air-breathing Vertebrata were formed like those in fishes, 

 by a modification of the true haemal arches of the trunk, the question 

 remained to be decided, which of the elements of such arches were 

 continued into the caudal region of reptiles, cetacea, &c. in order to 

 constitute those arches ; and Professor Owen had shown that the 

 solution was given by the adult perennibranchiate batrachia and by 

 the immature crocodiles, in which diapophyses and pleurapophyses 

 coexisted with such haemal arches in the tail : the laminae of these 

 arches therefore must be the haemapophyses as defined in his diagrams 

 of the typical vertebra, and consequently they must be the homo- 

 types of those haemapophyses which had received in the trunk the 

 special names of • ischia,' ' pubes,' ' abdominal ribs,' and ' sternal 

 ribs.' But the sternal ribs coexisted in the same vertebra with the 

 inferior exogenous processes from the centrum, to which processes 

 Dr. Melville proposed to transfer Professor Owen's name of ' ham- 

 apophyses.' Professor Owen had, however, proposed a proper name 

 for these commonly exogenous growths from the cortical part of the 

 centrum, as he had likewise found himself reluctantly compelled to 

 do for analogous exogenous processes from the neural arch, which 

 were independent of and superadded to the ordinary * diapophyses ' 

 and * zygapophyses.' Professor Owen called the attention of Dr. 

 Melville to a series of drawings in which he had proposed to illustrate 

 his descriptions of these accessory processes, and alluded to his de- 

 scription of them in the Catalogue of the Royal College of Surgeons. 



Professor Owen finally dissented from the definition of the ideal 

 vertebra, which Dr. Melville had adopted from his friend Mr. Mac- 

 lise. 



Professor Owen considered that a typical structure might be de- 

 parted from by excess as well as deficiency. As an example of such 

 excess, he regarded those vertebrae which, in subserviency to muscular 

 attachments, developed hypapophyses, anapophyses, metapophyses 

 and diapophyses, or which in like adaptive subserviency to stronger 

 union developed epizygapophyses, in addition to the ordinary prae- 

 and post-zygapophyses ; or which developed from the upper part of 

 the centrum epi-apophyses, which in the cranial vertebrae had received 

 the special denomination of clinoid processes, and were for the spe- 

 cial protection of an appendage to the neural axis. In certain human 

 crania these latter exogenous developments actually formed a secon- 

 dary and minor neural arch internal to or concentric wuth the larger 

 and normal neural arch ; and Professor Owen drew a diagram of a 

 section of such a vertebra, showing the small neural canal close above 

 the centrum (basisphenoid) of the parietal vertebra, answering to, or 

 homotypical with, the small haemal canal formed by exogenous 

 growths from the under part of the centrum (basi-occipital) of the 

 occipital vertebrae of the carp, and from the centrums of certain cer- 

 vical vertebrae of fishes and birds, and which Dr. Melville had trans- 

 ferred to his diagram of a thoracic vertebra, and made it to consist 

 of three distinct elements. Professor Owen stated that he had not 

 presumed to depart wholly from nature, either by addition or sub- 



