360 MALL. [VoL. XIV. 
walls of the abdomen, and from it we can make all of our 
counts. The segment above the ninth is usually the eighth, 
but occasionally the eighth and seventh combined, while the 
one lying upon the ribs belongs to the fifth and sixth, or sixth 
and seventh, or fifth, sixth, and seventh segments, as the case 
may be. The portion of the muscle below the umbilicus usually 
‘represents three segments, the tenth, eleventh, and twelfth, 
but occasionally a portion of the first lumbar may be included. 
It is of course understood that the numbers of the segments 
indicate from which myotomes they arose. 
The comparative studies of Ruge! show that the number of 
segments in the rectus increase as we pass down the scale of 
mammals, and the relation of the umbilicus to the segments 
changes in proportion to the number. As the number of 
segments increases, the umbilicus is pushed more and more 
away from the head. In man it is nearest the head, but when 
there is a variation in its position it is in the form of a 
reversion. Ruge’s Figs. 12, 13, and 14 illustrate this well, 
showing that the umbilicus may be below the tenth segment. 
I have shown in an earlier communication that in the shift- 
ing of the viscera during development thete is a fixed point 
opposite the first sacral segment, beyond which they do not 
pass. Everything descends towards this point, and those which 
go farther protrude into the umbilical cord. With the extreme 
shifting of the viscera there is a partial shifting of the abdomi- 
nal walls, which seems to be partly controlled by the fixed 
point opposite the sacrum. This lower and more fundamental 
fixed point appears to be the meeting point of two forces, one 
the movement from the head towards the tail, and the other in 
the opposite direction. The point is well established in embryo 
XXII, and may control to a great extent the further shifting 
of the abdominal muscles. If there is any meaning to this fixed 
point opposite the sacrum, it will be necessary to find that it lies 
farther and farther away from the head as we pass down the 
scale of mammals. 
After the ninth segment has become definitely located just 
above the umbilicus the portion of the muscle between the 
1 Ruge, Morph. Jahrb., Bd. xix, p. 376. 
