BY W. J. S. McKAY. 277 



small area occupied by the P. major), and from the aponeurosis 

 of the external oblique. 



Insertion. The muscle runs forward and outwards, lying 

 superficial to the postero-exterual border of the P. major. It 

 dives beneath the upper layer of the deep panniculus, and is 

 inserted on the superficial (ventral) surface of the tendon of the 

 P. major, its fibres being intimately related to the median layer 

 (Fig. 6, Pt. Q.) of the deep panniculus (see ante). 



Relations. The muscle at its origin is close to its fellow 

 of the opposite side. As it runs to its insertion it hides part of 

 the rectus. It does not reach, nor was it inserted on, the tendinous 

 intersection of the P. major as stated by Smith. It undergoes no 

 cleavage. 



It will be understood from the above descriptions that the dis- 

 position of the various layers of the pectorals and panniculus is 

 as follows : — 



In Echidna [a) superficial layer of [)anniculus ; (6) upper layer 

 of deep panniculus ; (c) upper layer of P. quartus ; [d) P. major ; 

 (e) deep layer of P. quartus ; (/) deep layer of deep panniculus. 



In OrnWiorhynchus (a) superficial layer of panniculus ; (b) upper 

 layer of deep panniculus ; (c) P. quartus and median layer of deep 

 panniculus ; (d) P. major, and deep layer of deep panniculus. 



Innervation. P. major, Nn. cervicales, iv., v., vi., vii. 

 P. quartus in Echidna from nerve to the P. major, and possibly 

 from the lateral cutaneous of the thorax. The same for 

 Ornithorhynchus (Figs. 13 et 16 ; 36, 37). 



Westling — Echidna : Innervation: Nn. cervicales v. and 

 vi. Oniithorhynchas, C. vii., C viii., D. i et ii. (Fig. 17, Pt.") 

 (For further remarks on iiinervation see post.) 



Westling — Echidna: " M. pectoralis major entspringt ingerader 

 Linie vom medialen Theile des Episternum, dem Sternum, dem 

 Processus xiphoideus und der Aponeurose des M. obliquus abdo- 

 minis externus ; der Muskel besteht aus zwei ziemlich getrennten 

 Theilen, einem vordei-n, kurzen und breiten, und einem hintern. 



