On the transverse processes of Hyperoodon bidens. 435 



Pileus effused, broadly reflected, pale fawn-coloured, with one 

 or two darker zones, clothed with rather spongy down behind 

 but in front radiato-striate ; margin undulated, very thin. Hy- 

 menium fawn-coloured, inclining to cinereous. Pores minute, 

 angular ; dissepiments thin. 



A resupinate form occurs with the margin slightly reflected, 

 and the pores darker and smaller. 



Allied to Pol. crispus, but very distinct. 



XLII. — Note on the Transverse Processes of the Two-toothed 

 Dolphin (Hyperoodon bidens). By Prof. Owen, F.R.S. &c. 



Two kinds of ' transverse processes ' are recognized in vertebrate 

 skeletons answering to the parts defined by Soemmei-ring, in the 

 human cervical vertebrae, as the ' radix prior, seu antica, e cor- 

 pore, processus transversi,' and the ' radix postica, ex arcu, pro- 

 cessus transversi ' : the so-called 'processus transversus' being 

 now known to consist of a rudimental rib (pleurapophysis) con- 

 fluent with the process from the body and the process from 

 the arch. Such processes are more developed and better defined 

 in the lower animals, where, instead of being 'anterior' and 

 ' posterior,' they are ' inferior ' and ' superior ' transverse pro- 

 cesses. I have proposed the single-worded term ' parapophysis ' 

 for the ' inferior transverse process ' or ' radix antica,' &c., and 

 ' diapophysis ' for the ' superior transverse process ' or ' radix 

 postica,' &c. 



The transverse processes in fishes are, as John Miiller and 

 others have shown, ' parapophyses ' ; those of Mammalia, where 

 they occur as a single pair, are ' diapophyses.' The Hyperoodon, 

 however, shows a structure which leads to the conclusion that 

 the transverse processes of the vertebrae with one pair of such are 

 ' parapophyses,' as in fishes. 



In the first to the sixth pairs of thoracic ribs the head of the 

 rib articulates with the interspace of the vertebral bodies (cen- 

 trums) and to contiguous parapophysial tubercles ; the tubercle 

 of the rib articulates with a diapophysis from the base of the 

 neural arch : in the seventh dorsal vertebra a well-marked par- 

 apophysis is developed from the centrum, for articulation with 

 the head of the rib, the tubercle still articulating with the dia- 

 pophysis above. In the eighth dorsal vertebra the diapophysis 

 abruptly ceases to be developed ; the tubercle of the rib, which 

 was reduced in the seventh pair, also disappears; and the 

 eighth rib articulates, like the ninth, by the head only to a 

 progressively elongating parapophysis : the long transverse prc- 



30* 



