38 THE HORSE IN HEALTH AND DISEASE 



The lumbar vertehrce comprise the six bones in the region of the 

 loins. The bodies are longer than those of the dorsal region. 

 The transverse processes are wide, flat plates, resembling an un- 

 developed rib. 



The sacrum, or croup, is composed of five vertebral segments 

 which are fused so as to form a single bone. It is triangular in 

 form and is wedged between the iha. Two surfaces, two borders, 

 a base, and an apex are presented for description. The dorsal 

 surface has a crest composed of the partially fused spinous processes. 

 The ventral surface is slightly concave from before backward. 

 The borders are formed by the fusion of the transverse processes 

 and present in front a facet for the articular surface of the ilium. 

 The base is represented by the anterior surface of the first sacral 

 vertebra. The apex is small and articulates with the first coccygeal 

 vertebra.^ 



The coccygeal vertehrce comprise all of the movable vertebrae 

 behind the sacrum. They vary in number, depending on the 

 development of the tail, and gradually diminish in size, so that the 

 spinal canal finally becomes a mere groove on the upper surface 

 of the bones. 



The thorax proper includes only the bones of the ribs and the 

 sternum. It is much compressed laterally in its anterior part, but 

 widens behind. 



The ribs number eighteen pairs, and are connected at one 

 extremity with the thoracic vertebrae and at the other with the 

 sternum. They are divided into eight pairs of true ribs and ten 

 pairs of false ribs. The true ribs articulate directly by means of 

 their cartilages with the sternum, while the false ribs articulate by 

 cartilaginous extensions. A typical rib is an elongated flat bone 

 with two surfaces and two extremities. The external surface is 

 convex and roughened; the internal, concave and smooth. The 

 dorsal end has three distinct parts, the head, neck, and tubercle. 

 The head is convex for articulation with the two dorsal vertebrae 

 above it. The neck is the constricted part below the head. 

 The tubercle articulates with the transverse process of the 

 corresponding dorsal vertebra. The lower end is enlarged 

 and has a rough cavity for the costal cartilage. The first rib 



'■ An observation recorded in Bulletin 117 of the Pennsylvania Agricultural 

 College showed that horses were higher at the withers than at the croup when 

 thin, but after having been "finished" they were higher at the croup. 



