Organs of Respiration and Circulation. 



589 



describe, will be at once recognised by a reference to the annexed 

 figures 10 to 13. In the first-named figure the under surface of 



the sternum of the ox is de- 

 ^^^' ^^' picted, and it will be observed 



that it is perfectly flat, conse- 

 quently it can be subjected to 

 pressure without inconvenience 

 to the animal when he is rest- 

 ing on the ground. On the 

 contrary, this part of the ster- 

 num of the horse has a thin 

 cartilaginous edge, similar in 

 appearance as well as in posi- 

 tion to the keel of a boat, see 

 fig. 12, which ill adapts it to 

 receive a similar pressure. In 

 both animals the sternum is 

 originally composed of several 

 bony pieces, which as age ad- 

 vances are more or less per- 

 fectly united together : these 

 pieces are, however, very differ- 

 ently arranged, so that in the ox 

 hone supplies the place of cartilage in the horse, and forms 

 the flat surface before mentioned. The loss of elasticity, and 

 consequently of motion, cartilage being highly elastic, is however 

 more than compensated for by the manner the first bone is united 

 to the second in the ox. In this animal, the first bone, manu- 

 brium, is attached by a synovial joint, which allows of a free 

 motion in various directions, but more particularly from side to 

 side; see a, fig. U. The cariniform cartilage in the horse (a, 

 fig. 12) is substituted for the manubrium with its synovial joint. 

 The arrangement here spoken of allows the anterior portion of 

 the thorax of the ox to yield the more readily to the respira- 

 tory movements, and likewise facilitates the curving of the lower 



Fig. 11. 



sternum of ox, inferior view. n. Tlie manu- 

 brium, fc. The ensiform cartilage. 



Lateral representation of the sternum of the ox. 



a. The. 



removed 



joint formed by the union of the first bone, manubrium ; the cartilage of the rib being partly 

 noved to brinjr it into view. b. The manubrium. c. The ensiform cartilage. 



