22 



Kitiialed uil tlic spol of tlie iHeiiibnuie. Indeed wc know, tliat willi 

 Urodele Amplnhia and witli Reptilia the abdominal wall is composed 

 of more muscles than witli Primates. The ontogeny and phylogeny 

 of the abdominal muscles of lower Vertebrates (Pisces, Amphibia, 

 Reptilia) has been accurately explained to us by the investigations 

 of Mai'kkk '). It is especially the structure of the muscular abdo- 

 minal wail of the urodele Amphibia that is of great interest for us ; 

 the abdominal muscles of Pisces still show very simple conditions, 

 whilst the conditions of the abdominal muscles of Anure Amphibia 

 and Reptilia can very well be deduced from those of Urodeles. 



Urodele Amphibia possess four collateral abdominal muscles. Most, 

 superficially are situated two muscles, the fibres of which have 

 an obliquely descending direction : a M. obliq. ext. superticialis'and 

 a M. obliq. ext. profundus. The direction of the fibres of these 

 muscles differs little ; that of the deep muscle is somewhat less oblique. 

 Under the Musculi obliq. ext. one finds a M. obliq. int. with an 

 obliquely ascending direction of tlie fibres, and abdominally from it 

 lies the M. transversus, the fibres of wliicli run in a transversal 

 direction. Maurer distinguishes these muscles in primary and second- 

 ary ones. The primary muscles: M. obliq: int., M. obliq. ext. prof, 

 and M. rectus profundus occur with the larva; the secondary ones: 

 M. obliq. ext. superfic, M. transv. and M. rectus superficialis come 

 into existence at the end of the larva-life by delamination of the 

 younger cells at the surface of the primary muscles. From the 

 development it is obvious, that the M. obliq. int. and the M. obliq. 

 ext. prof, are dorsaliy connected with each other in the myotome 

 and can never extend beyond the line of demarcation between the 

 ventral and the dorsal musculature, the lateral line; veii- 

 trally iioth muscles are connected in the M. rectus profundus. The 

 direction of their fibres changes here gradually from an oblique one 

 into the longitudinal one of the M. rectus prof. The M. obliq. ext. 

 superf. and the M. transv. however can extend dorsaliy from the 

 lateral line, and from the beginning tliey possess an aponeurosis 

 which runs before, resp. behind, the system of the Musculi recti to 

 the linea alba. 



') F. Mauher, ÜC'i- Aufbiia unci tlie EnUvicklung der voulralen Riirapfinuskulalur 

 bei den urodelen Amphibien und deren Bezichung zii den gleiclien Muskeln der 

 Selachiei- und Teleosticr. Morph. Jalirb. 18 Bd. 1892. 



F. Maurer. Die ventrale Bumiifmuskulatur der aiuuen Ampliibien. Morph. 

 Jabrb. 22 Bd. 1804. 



F. Maurer. Die ventrale Rumpfmuskulalur einigcr Replilien, eine verglcicliend- 

 anatomische Untcrsiicliung. Festschrift ziim 70 Geburtstagc von Carl Gegenbaur, 

 189G. 



