21 



What it. now tlie isigiiitioalioii llial imisl be altributed to tlii.s lucin- 

 braiie occiiiTing so constantly in monkeys? 



One might be inclined to regard the membiane as a condensation 

 of the intermuscniar connective tissue; for likewise in man one often 

 sees tliat from tiie tlimsj connective tissue between tiie abdo- 

 minal muscles fascial membranes can develop to incretise the solidity 

 of the abdominal wall. There are however objections that tell against 

 this view : in the first place it cannot be explained in this way. 

 why in many Simiae such a membrane does exist between the 

 M. obliq. ext. and the M. obliq. int.. but no vestige of fascial tissue 

 between M. obli(|. int. and M. transv. is to be found ; secondly it 

 cannot be comprehended in this way, why the membrane possesses 

 such distinct anatomical lines of demarcation ; thirdly the great 

 independence that this membrane possesses tells against this view. 

 With most Platyrrhini e. g. the membrane runs in the cranial part 

 behind the M. rectus, in the caudal [)art in front of it; it changes 

 consequently its course with regard to this muscle and moreover 

 independently of the abdominal muscles iietween which it is situated. 



From these objections appears distinctly, that the membrane may 

 by no means be regarded as a simple local condensation of inter- 

 muscular connective tissue. Most admissible it is to consider it as a 

 rudiment of a muscle that has existed on this spot with lower 

 vertebrates. With this hypothesis all the properties of the membrane 

 — as its sharp anatomical lines of demarcation, its independence — can 

 easily be explained. The correctness of this view is moreover 

 proved by a discovery with Siamang. With a Siamanga syndactylns 

 I found namely muscular fibres running in the membrane ; these 

 muscular fibres form a bundle of '^ mm. wide and 4.5 cm. long, 

 which bundle is situated between the point of the last rib and (he 

 crista iliaca. The fibres do however not originate in (he rib, but 

 about 74 *^'"- feudally from the point of the last rib the muscular 

 fibres appeal' in the membrane. The libres run almost vertically down- 

 ward, their direction corresponds with that of the fibres of the 

 M. obliq. ext. The libres are inserted into the crista iliaca, a little 

 behind the spina iliaca anterior. The muscle possesses moreover still 

 a smaller head, arising from the fascia luinbodorsalis. 



As now, in the direction of the ventral medianline, the membr. 

 interm. is directly connected with this muscle, and as moreover the 

 origin of the muscidar libi'cs is not situated at the last rib, iiut the 

 fibres ajipear in the membiane at a little distance caudally from 

 the rib, it is clear lh;it this nuiscle with Siamang is the last remain- 

 ing part of a muscle which, with ph\ loiiciielically older forms, was 



