r r r c 



«• r r 

 r < r r 



]8 ; '.- POULTRY DISEASES 



palate or roof of the mouth. It articulates with the pterygoid, 

 superior maxilla and premaxilla. The os pterygoideum or 

 pterygoid bone (9), articulates with the sphenoid and os 

 quadratum (10). The os quadratum articulates with the 

 temporal, maxilla, zygomatic and pterj^goid. The os auricu- 

 lare (11) is interposed between the maxilla and quadrate 

 bone. The atlas (13) or first cervical vertebra articulates 

 anteriorly with the condyle of the occipital bone and the axis, 

 the latter being located posteriorly. 



There are fourteen cervical vertebrae in the fowl, fifteen 

 in the duck, eighteen in the goose and twelve in the pigeon. 



The long column of cervical vertebrae serves as a sort of 

 balancing pole, and by changing in form and direction it 

 varif'S the center of gravity. In flying, the bird changes the 

 centi^r of gravity from the region over the legs to the region 

 of the wings. AYhen at rest the head and neck are thrown 

 backwards, carrying the center of gravity back over the legs. 

 The first cervical vertebra is the atlas. This is the smallest 

 of the vertebrae and is ring-shaped. Anteriorly it articu- 

 lates with the single condyle of the occipital bone. This 

 anterior articular surface is half-moon shaped and forms a 

 deep articular joint called a ball and socket joint. This 

 type of joint makes possible, movements in all directions. 

 The condyle of the occiput also touches an articular end of 

 the odontoid process of the axis or second cervical vertebra. 

 Posteriorly there are found two small lateral wings possessing 

 articular facets which articulate with similar facets on the 

 lateral wings of the axis. The posterior part of the body 

 is provided with an articular facet which articulates Avith a 

 similar articular surface on the anterior portion of the body 

 of the axis. 



The body of each succeeding vertebra articulates Avith the 

 one immediately anterior and i:>osterior to it. Between each 

 two is a pad of fibro-cartilage. Above these bodies and 

 below the neural spines, we find a large neural canal which 

 is occupied by the spinal cord. Between each two vertebral 

 segments in the cervical region, the neural canal is exposed, 

 due to the neural arches incompletely bridging the canal in 

 that location. This space is protected or bridged over ])y an 

 intervertebral ligament. 



The dor.sal spines of the cervical vertebra are very small, 

 the ventral are more distinct. The anterior oblique spines 

 are provided on their under sui'faces with articuhir facets, 

 which articulate with similar articular facets on the upper 

 side of the posterior olilique process of the verte))ral segment 

 in front. The ventral spine on the last cervical segment is 



