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. 



annifornt 

 Cartilage 



Fig. 24. — Steenum of Horse, Lateral View. 

 The sternebrse are designated by Roman numerals and the costal facets by ordinary figures. 



First 

 thoracic 

 vertebra 



First rib 



The dor so-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 

 sterni^ can be distinctly felt in the central 

 furrow of the breast. 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 l)ackward 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- 

 deus). This is a thin plate, connected in front 

 with the last bony segment by a relatively thick, 

 narrow neck, and expanding in nearly circular 

 form behind and laterallj^ Its dorsal surface is 

 concave, and gives attachment to the diaphragm. 

 The ventral surface is convex. The free margin 

 is very thin. 



Development. — At birth the sternum of the 

 horse consists of seven bony segments or sternebrse 

 united by intersternebral cartilages. The last two 

 sternebrse fuse in the second month, but the 

 others do not usually unite completely even in 

 old age. The sternebrse 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. 



'The manubrium stprni of man is equivalent, strictly speaking, to the cariniform cartilage 

 + the first osseous segment of the horse. 



Cariniform 

 cartilage of 

 sternum 



Fig. 25. — Anterior Aperture of Tho- 

 rax OF Horse. (After Schmaltz, 

 Atlas d. Anat. d. Pferdes.) 



