1893.] 



PllOF. G, 13. nOAVES OS HAPALE JACCHUS. 



1G9 



from the ventral aspect OMiug to the approxiiuatiou in the ventral 

 middle line of their parent (seveiith pair of) ribs, in the manner 

 customary for other Mammals. Variability in ossification of the 

 fully formed mesosternal segments of Mammalia, such as may 

 bring about irregularities of the steruebrse with a more or less 

 alternate disposition of the lower ends of the opposite sternal ribs, 

 is uo uuconunon phenomenon, especially among the Primates ; 

 but it rarely affects the presternum \ In the case under con- 

 sideration, the base of that segment was correspondingly asym- 

 metrical, repeating, in relation to the first mesosternal segment, 



Tie. 1. 



Fip. 2. 



8lcriiiiiu of lldpalc jd.cchas. viewed from the inner (dorsal) aspect. 1. Normal. 

 2. Abnormal. Adults, nat. size. 



ft'. Presternum, d". Mesosternum. st'". Post- or xiphisternum. 



the relations of this to its fellow next in order of succession 

 behind. The mesosternum, while retaining, in respect to the inde- 

 pendence of its constituents, a persistently embryoiiic condition, 

 had so far increased in width during growth that the transverse 

 diameter of each succeeding steniebra exceeded, at its narrowest 

 point, that oi^ the expanded base of its normal counterpart. 

 Comparison with thenorn)al adult (fig. 1) showed that the sternum, 

 as a whole, had undergone an increase in breadth proportionate 

 to reduction in length, due allowance being made for the occasional 

 presence of but four distinct mesosternal segmejits". AVhen 

 viewed from the inner aspect (fig. 2), the extreme regularity of 



' See the skeletons of llio Gibbon in the Museum of Natural Ilistorj, and of 

 tlic Orang in the Tcacliing Collection K. College of fcjeiencc, South Kensington. 

 ■' Mivart, P. Z. S. 1W5, p.rjfi8. 



