186 THE STRUCTURE OF MAN 



maintained, as the venous circulation in the lower limbs now has, 

 against the action of gravity. This justifiable assumption has led 

 me to investigate the intercostal veins in Man closely, by way of 

 ascertaining if they possess valves, and my observations in all 

 essentials confirm those of Henle recorded in his Handbuch der 

 Anatomic. That is, I found great variation both in the number 

 and the development of the valves, so that the impression of a 

 retrogressive condition became irresistible. 



It is well known that in other parts of the body, valves of 

 the veins appear in a reduced and evidently degenerating or 

 vestigial form, and also that in the embryo there arise many 

 more valves than attain complete development. [The valves of 

 the portal system are among the number thus suppressed, but 

 they may be occasionally retained. 1 ] 



THE SPLEEN 



Throughout the Mammalian series three lobes of the spleen 

 may be detected, viz. an anterior, a posterior, and a middle, all 

 of which vary greatly in size and form, in the various types. In 

 Marsupials the posterior lobe stretches far down towards the 

 rectum. In the Placental mammals the lobes are increasingly 

 reduced, and finally, in the Primates, the posterior lobe has 

 almost disappeared ; but the anterior and the median are repre- 

 sented even in Man, while the posterior lobe is in him reduced to 

 a projection of its margo obtusus (Klaatsch). 



The average weight of the spleen in the white races is said 

 to be 195, and in the black but 171 grs. 



1 [These valves are typically bicuspid. They are most numerous at birth, in 

 the vessels of the large intestine. After birth they disappear rapidly, and when 

 present in the adult they appear to be most abundant on the small intestine. Cf. 

 Hochstetter, Archiv f. Anat. und Phys., 1887 ; Anat. Abth., p. 137 ; and Bryant, 

 Boston Medical and Surgical Journal, vol. cxix. p. 400. Hyrtl long ago drew 

 attention (Sitzungsb, Wien. Akad., Bd. Ixi. p. 27) to the existence in the Rodentia 

 of a spiral valve-like fold within the portal vein.] 



