SKELETON OF THE WILD DUCK. VERTEBRAL COLUMN. 309 



in the thirteenth vertebra they have coalesced completely, 

 forming a prominent hypapophysis. In the succeeding 

 vertebrae this hypapophysis rapidly decreases in size. 



The fifteenth and sixteenth cervical vertebrae resemble the 

 succeeding thoracic vertebrae, having short thick centra and 

 prominent squarely truncated neural spines ; the sides of the 

 neural arches are very deeply notched. The fifteenth vertebra 

 has a short transverse process, perforated by a wide vertebrar- 

 terial foramen, but this foramen is absent in the sixteenth. 

 The transverse processes of the fifteenth vertebra bear two 

 facets for the articulation of the capitulum and tuberculum of 

 the rib. The sixteenth vertebra has its tubercular facet on 

 the transverse process, but the capitular facet is borne on the 

 centrum. 



The second or axis vertebra is small, and has the centrum 

 drawn out into a comparatively very large hypapophysis. The 

 posterior articulating surface of the centrum is saddle-shaped, 

 the anterior nearly flat : above it the centrum is prolonged 

 into the prominent odontoid process, which is shown by 

 development to be the detached centrum of the atlas. The 

 neural arch is deeply notched in the middle line in front, and 

 at the sides behind. It is drawn out posteriorly into a wide 

 massive outgrowth, which overhangs the third vertebra and 

 bears the downwardly-directed postzygapophyses. The pre- 

 zygapophyses are situated at the sides of the anterior end of 

 the neural arch, and look directly outwards. The transverse 

 processes are very slightly developed, and are pierced by the 

 vertebrarterial canals. 



The atlas vertebra is a very slight ring-like structure, 

 thickened ventrally and bearing in front a prominent concave 

 cavity for articulation with the occipital condyle of the skull. 

 Posteriorly it bears a more or less flattened surface for arti- 

 culation with the centrum of the axis. It surrounds a large 

 cavity partially divided into a larger dorsal portion, which is 

 the neural canal, and a smaller ventral portion which lodges 



