111 



both the processes, but without the little element which would unite 

 their extreraities. 



In the seventh cervical vertebra the upper transverse process only 

 exists, and the small rib is generally also absent. When the foramen 

 is present in this vertebra, it appears to be enclosed beneath simply 

 by the extension of a little osseous stylet from the under side of the 

 diapophysis to the body of the vertebra, just as the neck of one ot 

 tbe true ribs extends between the points where its head and tubercle 

 . are articulated; butwhether this stylet be autogenous or exogenous, 

 that is, developed from a separate point of ossification or not, I have 

 at present no means of ascertaining. 



I was led to remark on this subject through tbe accidentai dis- 

 covery in the skeleton of a Polecat (Mustela putorius) of a pair of 

 rudimentai ribs, or rather portions of ribs, moveably articulated to 

 the extremities of the transverse processes of the seventh cemcal 

 vertebra ; their length is exactly one-fourth of an inch of true bone, 

 besides a Httle cartilaginous appendage at the tip. In a second 

 specimen I searcbed for a similar peculiarity, but was unable to per- 

 ceive its existence. The two specimens were both malęs, of mature 

 age and robust dimensions, resembling each other in every particular. 

 This circumstance naturally led me to observe with considerable mi- 

 nuteness the skeleton of the Tbree-toed Sloth {Bradypus tridactylus), 

 in which the existence of nine vertebrse anterior to those formmg 

 part of the thorax has long been known ; and the discovery by Pro- 

 fessor Bell of rudimentai ribs articulated to the eighth and mnth of 

 the series renders that exceptional instance additionally interesting. 

 I therefore attentively perused the paper contributed by that leamed 

 naturalist to the first volume of the Society's Transactions. 



It may indeed appear presumptuous onmy part to dissent from the 

 conclusions which so eminent a professor has drawn from bis dis- 

 covery, but my observations led me irresistibly to the conclusion, 

 that if there is any essential distinction between the vertebrae of the 

 cervical and dorsal regions, the eighth and ninth vertebrae of the 

 Bradypus tridactylus mušt be classed among the former. 



The skeleton upon which my notes have been made is that con- 

 tained in the Museum of the Royal College of Surgeons ; it mušt be 

 perfectly mature, although the epiphyses at the distal extremities of 

 the ulna and radius stiU remain distinct, for every other epiphysis 

 has lošt all trace of separation from the bone to which it belongs, 

 and the characteristic anchylosis which unites most of the bones of 

 the foot is completely effected. The stemal ribs are all perfectly 

 ossified ; the first four of them are anchylosed to their corresponding 

 vertebral ribs, and the first one also to the manubrium stemi ; — so 

 small, comparatively, is the amount of respiratory action required by 

 this slow-moving quadruped. 



The differences existing between the eighth and ninth vertebrae 

 and those immediately above them are most clearly and accurately 

 described by Professor Bell ; sūrely it can hardly be necessary here 

 to quote his \vords ; but on comparing either the description that he 

 has given, or the skeleton itself, with the cerncal vertebrae of almost 



