ANATOMY OF THE HORSE. 15 



Lateral Surfaces. Thick anteriorly, growing thin posteriorly, 

 and presenting slight protuberances, (corresponding to the ver- 

 tebral transverse processes,) which serve for the attachment of 

 the sacro-iliac ligaments. 



Base. Composed of a middle- and two lateral parts. The 

 middle presents a convex articulatory surface, transversely oval, 

 for adaptation to the last lumbar vetebra ; surmounted by two 

 articulatory processes, between which are received the two last 

 of that name of the loins ; and having on its sides two notches 

 of conjugation for the last pair of lumbar nerves. The lateral 

 or anterior transverse processes, broad, thick, and projecting, 

 and triangular in figure, point forwards and upwards as well as 

 outwards : superiorly, they have two surfaces of articulation for 

 the ossa ilia; anteriorly, two others which unite with the last 

 transverse processes of the loins. 



Apex. Presents* also an oval surface, which articulates with 

 the foremost bone of the tail ; having on its sides two notches, 

 for the fifth pair of sacral nerves ; and, farther removed out- 

 ward, two little posterior transverse processes. 



The Sacral Canal for the spinal marrow is triangular in 

 figure, and gradually contracts its diameter from before back- 

 wards. 



Development. In the young subject this bone consists of five 

 distinct and separable pieces, united, one to another, by a fibro- 

 cartilaginous substance which in the adult is converted into 

 bone. 



THE TAIL-BONES. (oSSA COCCYGIS.) 



Situation. Behind the sacrum, to which the coccyx forms an 

 appendix. 



Fonn. (Of the coccyx entire.) Conical, elongated, and more or 

 less curved. 



Co)for?nation. The coccyx or tail is constituted of several 

 small bones resembling vertebrae, varying in size and develop- 

 ment, and also in number from thirteen to eighteen. 



Division. As a whole, the coccyx presents for consideration 

 two surfaces, two borders, a base, and an apex. 



Superior Surface — Convex. The two and sometimes three 

 first bones possess complete bony arches, from which arise one or 

 two spinous eminences giving attachment to the erectores coccy- 

 gis, and consequently they possess an uninterrupted spinal canal ; 

 in the following two or three pieces, the spinal arch becoming 

 gradually more defective, the closed canal degenerates into a 



