1126 
crossing of the Mm. recti began but was not entirely accomplished, 
the bending of the M. rectus is discernible at a certain level, while 
at a lower level, where the crossing had already been partly accom- 
plished, the connection between the two pieces of the M. rectus has 
been abolished. 
How it is that in the Simiae and in man a bent piece of the M. 
rectus is liberated as a M. pyramidalis, is not so easy to under- 
stand as it is in Inseetivora. But, also in other regions of the human 
system it occurs that the portion of a muscle with U-shaped inser- 
tion, the insertion being one of the arms of the U, becomes inde- 
pendent. This e.g. may be the case with the pars abdominalis of 
the M. pectoralis major. 
With this exposition of the origin of the M. pyramidalis in man 
several facts are in perfect harmony. First of all the fact that 
Santorini and other authors have established that the insertion of 
the M. rectus into the Os pubis is narrow, when the M. pyramidalis 
has a broad origin in this skeletal bone and conversely. In agree- 
ment with this is also the fact that some fibres of the M. rectus 
are regularly inserted into the inferior part of the linea alba, as is 
described by Nicatsp'), as the rectus must of necessity obtain an 
insertion, along the previous line of flexion, into the linea alba, 
when the same happens with the M. pyramidalis. i 
Because the function of the M. pyramidalis is very inconsiderable 
this muscle disappears in many cases either on one side or on either 
side, the only indication of its earlier existence and mode of origin 
then being the insertion of fibres of the M. rectus into the inferior 
part of the linea alba. 
The question may be asked why in some animals the insertion 
of the M. rectus is U-shaped. In this respect there may be relation- 
ship between the breadth of the M. rectus on the one side and 
on the other side the dimensions, the form and the size of the 
pelvis i.e. the space for insertion. This, however, requires further 
investigation. We only wish te observe that among the half-apes the 
M. rectus has a simple, recti linear insertion in the Lemurinae and 
that in the other half-apes the M. rectus presents a more compli- 
cated mode of insertion. This, no doubt, has something to do with 
the fact recorded by Weber’) that the Lemurinae have a wide 
pelvis: ,,Gegeniiber dem weiten Becken der Lemurinae, haben die 
nicht-madagassichen Prosimiae ein enges Becken.” 
!) Eister. Die Muskeln des Stammes, p. 565 
2) M. Weser. „Die Säugetiere”. p. 747. 
