SKELETON OF BIMANA. 



,55 



Deveiopment of human steniuni. cxxi 



ib. e, s, s, coalesce to form the ^ gladiolus ' or ' body ' of the 

 sternum : the sixth piece, which commonly remains distinct, is the 

 ' xiphoid appendage, x.' The parts of the sternum are usually 

 developed each from a single centre, as at Z», i , 2, 3, 4 : but occa- 

 sionally, and usually the lower ones, are developed from a pair of 

 centres, c, 1, 3, 4, as in the 

 broader breast-bone of the 

 Gorilla and Orang : a fissure 

 or foramen may persist as 

 an anomaly, fig. 364, d, s : 

 but the union of the pairs 

 transversely usually precedes 

 that in a longitudinal direc- 

 tion. In fig. 364, a repre- 

 sents the primordial cartilages 

 of the dorsal haemapophyses 

 and spines ; ib., Z> and c, 

 varieties in the ossific nuclei. 

 Occasionally a pair of tuber- 

 cles, ib. *d *, indicate epister- 



nal rudiments.^ The second to the seventh pairs of costal cartilages 

 articulate with the sternal body : the second between it and the 

 manubrium : the seventh between it and the xiphoid appendage : 

 the first to the manubrium exclusively. The ribs which thus join 

 the sternum are called ' true ;' 

 the five remaining pairs ' false,' 

 and of these the last two are 

 ' floating ' ribs. The propor- 

 tions of the dorsal pleurapo- 

 physes, or bony ribs, and 

 their degrees of curvature, 

 are shown in fig. 363, in their 

 position after deep expiration. 

 In each is distinguished the 

 ' head,' fig. 365, c, the ^ neck,' 



/, the ' tubercle,'^, and the ' shaft,' the part of the curve marked 

 h being called the ^ angle : ' <:/ is the ' sternal,' or rather hasmapo- 

 physial end to which the shaft usually slightly expands. The first 

 and last three ribs have a single articular surface on the head : in 

 tlie rest it is divided into two facets. The tubercular articular 

 surface is wanting in the last tAvo pairs. When the pleurapophyses 



365 



The fourth rib: Human. 



' cviir. p. 91. 



