8 



end, and by their other end to the haemal spine or sternal bone, which com- 

 pletes the haemal arch below ; the condition of the great expansion of this 

 arch being the same as that noticed in the thoracic vertebra of the bird. 



Prepared by Prof. Owen. 



31. A cervical vertebra of the Dugong, in which the pleurapophyses as well as the 

 neurapophyses have coalesced with the centrum, about which, therefore, there 

 are three canals, the upper or neural one for the spinal chord, and two lateral 

 ones for the vertebral arteries. The haemal canal is not circumscribed by bone. 

 This vertebra is singularly flattened in the direction of its axis ; the neural canal 

 is capacious, which is characteristic of the mammalian trunk vertebras : there 

 is no neural spine. Presented by Sir T. Stamford Raffles, F.E.S. 



3~. The fifth cervical vertebra of a young Rhinoceros, showing the anterior convex 

 articular end and the posterior concave end of the centrum, as distinct epi- 

 physes of that element ; which is a characteristic mode of its development in 

 Mammalia. On removing these epiphyses, traces of the suture between the 

 neurapophyses (n) and the centrum may be recognised, showing that the para- 

 pophyses (jy) are developed from the centrum, and the diapophyses (d) from 

 the neural arch. The pleurapophyses or cervical ribs have, however, com- 

 pletely coalesced with the parapophyses and the diapophyses, circumscribing 

 therewith the canals for the vertebral arteries. Purchased. 



33. The third cervical vertebra of a nearly full-grown Echidna, in which Monotre- 

 matous Mammal the pleurapophyses (pi) retain longer than in the higher 

 orders of that class their primitive distinctness. The proportion of each ' ver- 

 tebral foramen' contributed respectively by the parapophysis, diapophysis and 

 pleurapophysis is clearly shown in this example. The pleurapophysis is short 

 and broad, and has both ' head ' and ' tubercle.' The neural canal has the cha- 

 racteristic mammalian capacity ; there is a short neural spine. 



Prepared by Prof. Owen. 



