25 



described with tiie help of lext-figures, represeiUiiig diagrainuiatic 

 transversal sections throiigli the sheath. In all sections tlie M. obliq. 

 ext. is represented by a dotted line, the Membrana abdominis inter- 

 media by a point-dash-line, the M. obliq. int. by an iiniiderriiiited 

 line, and the M. transversns by a dash-line. 



The stnictnre of the rectal sheath of Primates shows considerable 

 differences. It is however possible to nnite all those cases nnder 

 one point of view; it will appear that in this way a more primitive 

 condition and relations that have removed from the original condition, 

 can be distinguished. The succession in which the rectal sheath of 

 the different Primates will be described is such, that I shall begin 

 with a condition of which afterwards it will appear, that it is the 

 most original one. and conclude with the description of the structure 

 of the sheath of such monkeys, which have farthest removed from 

 the primitive condition. 



Fig. la re[)resents a transversal section through the sheath of the 

 M. rectus of Ateles paniscus, close under the caudal edge of the 



/ 



d. 



Fig. 1. Ateles paniscus. 

 L. a. = Linea alba. 

 R. = Muse, rectus abdominis. 



1. = M. transversus abdominis. 



2. = M. obliquus internus abdom. 



3. = Mcnibiaiia abdominis intermedia. 



4. ^= M. obliquus externus abdom. 



Fig. 2. Ateles hypoxanthus. 



