1124 
Now concerning the M. pyramidalis the following facts may be 
pointed out. 
The M. pyramidalis in man is a small triangular muscle in the 
anterior abdominal wall, arising from the pubic crest in front of 
the rectus muscle. It is directed obliquely upwards, to be inserted 
for a variable distance into the linea alba. Some superficial fibers 
are also inserted into the posterior side of the ventral leaf of the 
rectus-sheath *). This muscle is lodged right in front of the M. rectus 
and is separated from it only by a thin layer of loose connective 
tissue. Yet the connective tissue between the two muscles sometimes 
seems to become a solid membrane, for we read in EisLER’s *) work: 
“In der Regel findet sich zwischen Pyramidalis und Rectus nur 
eine diinne Schicht lockeren Bindegewebes, doch schiebt sich gele- 
gentlich von latera her ein aponeurolisches von der ventralen Rectus 
scheidewand im besonderen von der Aponeurose des M. transversus 
abdominis abgespaltenes Blatt zwischen beide, ohne aber eine voll- 
ständige Abschlieszung des Pyramidalis herzustellen”’. 
Krausk*) maintains even that the latter condition is the rule. Since, 
however, the obturation (Abschlieszung) as HisLer remarks, js never 
complete, and occurs only exceptionally, anyhow is not constant by 
far, -— witness the different opinions prevailing in this respect — 
it does not seem probable that the obturation is effected by a true 
aponeurosis. 
The M. pyramidalis is lacking bilaterally in + 16°/, of the Euro- 
peans, in half the other cases it occurs only unilaterally. Further- 
more the M. pyramidalis is absent in approximately 10°/, of the 
Negroes and 4°/, of the Japanese. 
The following remarks are still given by Santorini, CRUVEILHIER, 
Quain and GRGENBAUR. In the absence of the M. pyramidalis the 
caudal end of the M. rectus is broader and stronger; conversely, 
MacALISTER *) reports that the insertion of the M. rectus is narrow 
when the M. pyramidalis is strongly developed. We shall see that 
these relations are of some consequence. 
In man the aponeurosis of the M. obliquus internus continues as 
far as the linea alba, without any junction between this aponeurosis 
and the M. pyramidalis, as in the case of Didelphys. The direction 
of the fibres of M. pyramidalis and of M. obliquus internus differs 
rather much; moreover the aponeurosis of the M. transversus is 
1) Erster. Die Muskeln des Stammes. p. 572. 
3) KIsLer l.c. 
3) Krause. Handbuch der menschlichen da 1879 Bd Il, p. 242. 
4) Hisuer lc. p. 574. 
