56 OUTLINES OF EQUINE ANATOMY. 



It is slightly concave from before backwards, is widest 

 anteriorly, and decreases in size posteriorly ; on either side 

 it slopes upwards and outwards, presenting the inferior roiv 

 cf foramina (subsacral), which are much larger than the 

 .superior. Internally placed to the foramina the lateral 

 sacral, arteries run along this portion of the bone. The 

 apex consists of a somewhat rounded and slightly concave 

 .articular surface, surmounted by a small ring, presenting on 

 either side a small transverse, superiorlj^ a superior spinous 

 process. It articulates with the first coccygeal vertebra. 



THE COCCYGEAL VERTEBRiS 



from thirteen to eighteen in number, occupy the pos- 

 jterior part of the vertebral column, and are small 

 bones in which the different parts of a vertebra assume a 

 more and more rudimentary form from before backwards, 

 so that while the first presents a body, ring, and small 

 2)rocesses, the sixth presents only a body with two pedicles 

 and small transverse processes ; the posterior coccygeal hones 

 ..are merely small bony masses, elongated from before back- 

 wards, enlarged at each extremity, where they become 

 united with their fellows by fibro- cartilage. The pos- 

 terior bones only become ossified late in life, so that the 

 number of these vertebrae varies with age. They all 

 present both anteriorly and posteriorly convex articulatory 

 surfaces to their bodies. In consequence of this, mobility 

 of the vertebral column here attains its maximum, but the 

 want of a regular set of processes renders these false 

 Tertebrse ; superiorly they afford attachment to the 

 levatores coccygis ; inferiorly to the clepressores ; laterally 

 to the curvatores. The anterior bones also afford attach- 

 ment to ischio-tibialis and to compressor coccygis. 



THE RIBS, COST^, 



together with the sternum and the cartilages of elongation 

 .form the haemal arch of the dorsal vertebral segments. 

 They are elongated bones, extending from above down- 

 wards from the lateral parts of the dorsal vertebrae. 

 Though they have a longitudinal axis greatly exceeding 

 either of the transverse axes, yet as they present no medul- 

 lary canal nor marked distinction of shaft and extremities, 



