140 



216 ANATOMY OF VERTEBRATES. 



I[ \ 01^ lower half of the myocommas in the 



trunk, fig. 140, 6, has been held to represent 



8 1^ iW - the ohUquus externus ahdominis ; but, as it 



is segmented by aponeurotic prolongations of 

 the short jileurapophyses, both in the abdo- 

 minal and caudal regions, it is more like a 

 series of intercostals. The broad, thin, car- 

 ncotendinous sheets, called ' external ' and 

 ' internal oblique ' muscles in Mammals, hav- 

 ing their fibres running in opposite directions, 

 may, indeed, be referred to the same system 

 of segmental trunk-muscles ; but this grade 

 of dliferentiation is not reached in Fishes 

 and fish-like Batrachians. The medial parts 

 of the hremal myocommas are more distinct, 

 and show more of the character of a longi- 

 tudinal nmscle with tendinous intersections, 

 like the ' linear transversa3 ' of the human 

 ' rectus abdominis ;' and this muscle is one 

 of the determinable homologues of a recog- 

 nisable tract of the myocommas of the fish 

 and newt. In the Salamander, however, 

 the tract, fig. 141, ?, is as superficial as that 

 part of the sheath of the ' rectus abdominis ' 

 in Mammals ; and it forms a corresponding 

 ]iart of the sheath of a deeper-seated longi- 

 tudinal muscle, fig. 141, 7. Both 7 and 8 

 are specialisations of the lowest hcBnial por- 

 tions of the myocommas : thej' are anteriorly 

 resolved, or continued, as in Fishes, into 

 muscles acting upon the scapular, hyoidcan, 

 and mandibidar arches. The jiuholnjoidcus, 

 7, arises from the pubis and outer part of 

 the gristly ha>mapophysis, or Y-shaped 

 cartilage, fig. 113, d\ it runs forward 

 in a sheath, analogous to that formed 

 by the aponeurosis of the external and in- 

 ternal oblique muscles of jMaunnals, and is 

 inserted into the ceratohyal. The muscle, 

 s, called rertus ahdoiiiiiiis, by Funk,' has its 

 attacluncnt to the pubis througli the medium 

 <if the Y-slinpcd cartilage, wliich represents 

 llie marsupial bones and tendinous ' pillars 

 t»f the abdominal ring" in jNIannnals : it is 



