On the transverse processes of Hj-peroodon 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 occm*s with the margin slightly reflected, 

 and the pores darker and smaller. 



Allied to Pol. crispns, but very distinct. 



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

 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 Soemmerring, in the 

 human cerWcal vertebrse, 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 fii-st 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 pru- 



30* 



