46 



THE SKELETON OF THE HORSE 



The first four are elliptical in outline with the long diameter vertical, and are sep- 

 arated by considerable regular intervals. The others are progressively smaller, 

 more circular, and closer together. The area below these cavities gives attachment 

 to the pectoral muscles. 



jLiphoid cartilaq 



\luJ^ Carl ni form 

 Cartilage 



°- i 



■3 o 



Fio. 24. — Sternum of Horse, Lateral Vif.w. 

 The sternebrae are designated by Roman numerals and the costal facets by ordinary figi 



First 

 thoracic 

 vertebra 



First rib 



The dorso-lateral borders separate the dorsal and lateral surfaces. They give 

 attachment to the lateral branches of the sternal ligament. 



The ventral border forms the prominent keel-like crest of the sternum (Crista 

 sterni) which may be felt in the living animal; it fades out behind. 



The anterior extremity or manubrium 



L sterni^ can be distinctly felt in the central 



furrow of the l)reast. It consists of a laterally 

 compressed cartilaginous prolongation, commonly 

 called the cariniform cartilage. Its lateral surfaces 

 ^^ are flat and furnish attachment to muscles of the 



breast and neck. The ventral border is rounded, 

 and is continued backward on the body of the 

 bone. The dorsal border is concave and has an 

 articular cavity for the first pair of costal cartil- 

 ages. 



The posterior extremity is formed by the 

 xiphoid or ensiform cartilage (Processus xiphoi- 

 tleus). This is a thin j^late, connected in front 

 with the last bony segment by a relatively thick, 

 narrow neck, and expanding in nearly circular 

 form behind and laterally. Its dorsal surface is 

 concave, and gives attachment to the diaphragm. 

 The ventral surface is convex. The free margin 

 is very thin. 



Development. — At l)irth the sternum of the 

 horse consists of seven bony segments or sternebrae 

 united by intersternebral cartilages. The last two 

 sternel)ra3 fuse in the second month, but the 

 others do not usually unite completely even in 

 old age. The sternebrae consist of very vascular 

 spongy bone covered by a very thin layer of com- 

 pact substance. The adult sternum thus con- 

 sists to a very considerable extent of persisting 

 cartilage, viz., the intersternebral cartilages, the ventral keel, and the extremities; 

 in old age these undergo partial ossification. 



Cariniform 

 curtilage of 

 sternum 



Fig. 25. — Anterior Aperti-re ov Tho- 

 rax OK HoR.SE. (After Schmaltz, 

 Atlas d. Anat. d. Pfer<les.) 



'The marml)riiiin sterni of man is eiiuivalcnt, strictly speaking, to the cariniform cartilage 

 + the first osseous segment of the horse. 



