1893.] 



PEOF. G. B. HOWES OX HAPALE JACCUUS. 



169 



irom the ventral aspect o^\■ing to the approximation in the ventral 

 middle line of their parent (seventh 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 sternebrse A^ith a more or less 

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

 is uo uncommon phenomenon, especially among the Primates ; 

 but it rarely affects the presternum*. In the case trader con- 

 sideration, the base of that segment was correspondingly asym- 

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



Fig. 1. 



Fig. 2. 



Sternum of Hajiale jacchus. viewed from the inner (dorsal) aspect. I. Nonnal. 

 2. Abnormal. Adults, nat. size. 



s.t\ 



Presternum, st" . Mesosternum. st'". Post- orxiphiBtemum. 



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 embryonic condition, 

 had so far increased in width during growth that the transverse 

 diameter of each succeeding sternebra exceeded, at its narrowest 

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

 Comparison w ith the normal 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 segments \ When 

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



' See the skeletons of the Gibbon in the Museum of Natural History, and of 

 the Orang in the Teaching Collection E, College of Science, South Kensington. 

 2 Mirart, P. Z. S. 1865, p. .568. 



