392 



2193. The right calcaneum. 



Its posterior half is flattened vertically. 



2194. Three toe-phalanges. 



The following are parts of the same skeleton of a Beaver (Castor canadensis) : 



2195. The last cervical and first dorsal vertebrae, with the left rib, showing the 

 extent to which the head articulates with the last cervical, and the cavity in 

 the much-expanded diapophysis of the dorsal which receives the tubercle of 

 the rib, and which is strengthened anteriorly by the abutment of the perfo- 

 rated transverse process of the last cervical. The extremity of this process is 

 an epiphysis : the articular ends of the centrums are also epiphyses. 



2196. The fourth dorsal vertebra, with the left rib attached, showing the extent of 

 the head which articulates to the vertebra in advance, and the attachment of 

 the tubercle to the diapophysis. The deep excavations on the upper surface 

 of the centrum leading to the vascular canals are well shown. 



2197. The sixth dorsal vertebra, with the left rib attached, showing the develop- 

 ment of the accessory tubercle above the diapophysis. 



2198. The eighth to the twelfth dorsal vertebrae, inclusive, of the same Beaver; 

 showing the development and separation of the accessory tubercle from the 

 diapophysis, and its progressive transformation into the anapophysis and 

 metapophysis. This is accompanied with a progressive diminution of the 

 diapophysis, which ceases to articulate with the rib in the eleventh ver- 

 tebra. 



2199. The sacrum of a Canada Beaver (Castor canadensis), vertically bisected. 



It shows the epiphyses of the centrums and the small cavities between them, indicating 

 the remnant of the intervertebral substance in the otherwise anchylosed vertebrae : also the 

 perforation directly through the neurapophysis, anterior to the smaller conjugational foramen. 



Hunterian. 



