1030 



THORAX. 



lowed out for their cartilage. 



Fig. GGG. 



ence to the spine. But the relation of these lowed out for their cartilage. As the ribs 

 torsions to the spine are different : the pos- become more perfectly developed, for in- 

 terior torsion is relative to the spine late- stance, the 5th, 6th, 7th, and 8th, the an- 

 rallv, while the anterior torsion relates to terior extremity is broader, but not more 

 the" spine more in the antero-posterior direc- deeply hollowed out than some of the other 

 tion ' they both conspire to increase the obli- ribs, which are less perfectly developed, as in 

 quity of the rib in one given direction, from the 2nd and 3rd, or 1 1th ribs. This extremity 

 above downwards. is most pointed in the 12th rib. 



The torsion of the 1st rib, we have noticed, 

 is directed in a contrary direction to that of 

 other ribs ; and we have observed that the 

 presence of torsion in general favours 

 muscular traction: but the 1st rib is an 

 exception to this ; here the torsion exists 

 only between its two chief articulating pro- 

 cesses, the head and the tubercle : in the 

 other ribs the torsion is between the tu- 

 bercle and the body of the bone. The pos- 

 terior torsion of the 1st rib appears to be 

 merely destined to afford the head a more 

 complete attachment to the body of the one 

 vertebra (the 1st dorsal) to which that rib 

 is fixed. A posterior torsion, in this short 

 rib, is not needed for muscular traction, be- 

 cause here the scaleni are placed in the most 

 favourable position nearly at an angle of 

 90 with reference to the body of the bone 

 in question, while their other insertion into 

 the cervical vertebras facilitates the most ex- 

 tensive and favourable means for its mobility, 

 independently of any favouring twist in the 

 rib for that purpose. 



(4) Surfaces (special differences). The 

 thorax being conical, or somewhat barrel- 

 shaped, it follows that the surfaces of 

 the ribs, like the hoops of a very spherical R e i at i on O f the ribs to the spine in angular curvature. 

 barrel, must gradually change their direc- 

 tion ; thus the surfaces of the 1st rib are (b) Posterior extremity. The posterior ex- 

 nearly superior and inferior, this bone forming tremity of the rib is more complicated, and 

 the lid to the thorax, while the surfaces of the h as certain named parts, as the head, neck, 

 6th or 7th rib are external and internal, and as tubercle, and anjjle, all of which become niodi- 

 we proceed downwards to the 10th, llth, and fi e d as we pass from above downwards. Their 

 12th ribs, the surfaces are again slightly differences may briefly be noticed, 

 tending towards a superior and inferior po- 

 sition, so that the internal surfaces of the 1st 

 and 12th ribs are directed somewhat towards 

 each other. The body of the rib, or that 



}sl Of the /iead.~ On the head of the rib, 

 articulating with the vertebrae, a surface or 

 facet is formed. The 1st, the llth, and the 

 12th ribs articulate each with the body of one 



part which covers the lung laterally, and the vertebra, and therefore they have one arti- 



anterior and posterior extremities, have also culating surface. All the rest articulate each 



their surfaces inclined in different directions. w ith the bodies of two vertebrae, and they 



Thus, take a perfect rib, say the 7th, laterally consequently have two such articulating sur- 



to the thorax the two surfaces are internal faces as already described. The head of the 



and external, while at the anterior end they ] s t rib is relatively larger than that of the 



are directed external surface, forwards and 

 downwards ; internal surface, upwards and 

 backwards ; at the posterior end, external 

 surface, upwards and backwards ; internal 

 surface, downwards and forwards. This is 

 produced by their respective torsions. In 



others. For the most part, as the ribs in- 

 crease in size, the head likewise increases, 

 so that in the best developed rib the head and 

 its surfaces are most perfectly formed, dege- 

 nerating again to the 12th rib. 



2nd Of the neck. The neck being that 



/ _ 1 I i \_ . .,!_* 1 ._ 4.1 ,-. C 



some of the lower animals the ribs overlap part of the rib between the articulation of 



each other like the tiles of a house; this 

 sometimes threatens in man, particularly in 

 diseases of the spine (fig- 666.), when they 

 closely approach each other. 



the rib with the bodies of the vertebra, and 

 that with the transverse process, and these 

 points differing but little in their distance 

 from each other in the dorsal vertebra;, it 



(5) Specific differences of the extremities of follows that the absolute length of the neck 



the ribs. The greatest difference is in the of the different ribs is nearly the same. The 



posterior end of the rib. The anterior pro necks of the ribs differ in their thickness, ac- 



senting little difference. cordingly as their respective ribs increase or 



(si) Anterior extremity. These are all hoi- diminish iu size; therefore, in the middle 



