THE TIIOEAX AS A WHOLE. 



2D- 



usually foiined in connection with the transverse process of the first lumbar 

 vertebra, or occasionally with the seventh cervical : in the latter case the addi- 

 tional rib has usually a double attachment, viz., to the body and transverse pro- 

 cess of the vertebra outside a vertebrarterial foramen (see fig. 21, 4, v, v, and 

 8, CO. 



The costal cartilages unite the ribs to the sternum. Their 

 breadth diminishes gradually from the first to the last, whilst their 

 length increases as far as the seventh, after which they become gradually 

 shorter. Their line of direction varies consideral^ly. The first 

 descends a little, the second is horizontal, and all the rest, except the 

 last two, ascend more and more fi'om the rib towards the sternum as 

 they are situated lower down. The external or costal extremity, convex 

 and uneven, is implanted into and united with the end of the corre- 

 sponding rib. The internal extremities of the upper seven (except the 

 first) are smaller than the external, somewhat pointed, and fit into 

 the corresponding angular surfaces on the side of the sternum, with 

 which they are articulated in synovial cavities. Each of the cartilages 

 of the first three asternal ribs becomes slender towards its extremity, 

 and is attached to the lower border of that which is next above it. The 

 last two are pointed and unattached. 



The first cartilage, which is directly united to the sternum without 

 articular cavity, usually becomes more or less ossified in the adult male ; 

 and the others likewise exhibit a considerable tendency to ossify in 

 advanced life. This tendency is not so great in the female, in whom 

 costal respiration is generally more extended than in the male. 



THE THOEAX AS A WHOLE. 



The bony thorax is of a somewhat conical shape, with convex walls. 

 Fig. 24. — Fkont view of the Thor.\x, 



SHOWING THE StERNUM CoSTAL CARTI- 

 LAGES, Ribs, and Dorsal Yertebr,!:. i 



1, the manubrium, or first piece of the 

 sternum ; 2, is close to the place of union 

 of the first costal cartilage ; 3, the clavicular 

 notch ; 4, the middle of the body of the 

 sternum ; 5, the ensiform jirocess ; 6, the 

 groove on the lower border of the ribs ; 7, 

 the vertebral end of the ribs ; 8, the neck ; 

 9, tubercle ; 10, costal cartilage ; 12, the 

 first rib ; 13, its tubei'osity ; 14, the first 

 dorsal vertebra; 15, the eleventh ; 16, the 

 twelfth rib. 



Its upper opening is contracted, 



and bounded by the first dorsal 



vertebra, the first pair of ribs, and 



the manubrium of the sternum. Its 



inferior margin slopes downwards 



and backwards on each side from 



the ensiform cartilage to the 



twelfth rib. Its longitudinal axis 



is directed upwards and somewhat backwards. Its transverse diameter, 



at its widest part, greatly exceeds that from before backwards. The latter 



is shortened in the middle line by the projection of the vertebral column, 



