284 SHOULDER-GIRDLE IN MONOTREMES, 



CuTiER and Laurillard take the clavicular portion to be part 

 of the P. major, and the posterior portion as " deltoide," or 

 "sous-acromio-hum^rien" (Plate 266). 



CouES describes the clavicular portion of the deltoid as part of 

 the P. major (see ante), and describes as " anterior part of the 

 deltoid," the true epicoraco-hu moral ; he describes a scapular 

 portion. 



Westling makes the following remarks on the pectoral and 

 deltoid : — " The anterior portion of the deltoid presents a note- 

 worthy similarity to the clavicular portion of the M. pectoralis of 

 the OrnWwrhynchus, which part as such is absent in the Echidna. 

 Its origin, position and innervation point to an homology between 

 these muscles [i.e., between the anterior portion of the deltoid of 

 the Echidna and the clavicular portion of the pectoralis of Orni- 

 thorhynchus). I must, however, leave the point undecided for 

 further investigation whether, since the nerve supply to the P. 

 major of Ornithorhynchus is furnished by a different nerve trunk, 

 has the latter muscle originated through a blending of separate 

 muscles, or, is the condition found in Ornithorhynchus the primary 

 one, the deltoid having been differentiated from the pectoralis. 



Remarks on the P. major, P. quartus, and Clavicular Deltoid. 



Up to the present time, as far as we are aware, the clavicular 

 portion of the deltoid in Echidna has been clearly differentiated 

 from the pectoralis major since Mivart's paper appeared in 1866 ; 

 although he did not base his conclusions on the nerve supply to 

 the muscles. In Ornithorhynchus, on the other hand, the clavi- 

 cular portion of the deltoid has always been taken as representing 

 the clavicular portion of the P. major. The view that we have 

 arrived at is as follows. That the muscle described by Mivart 

 and others in Echidna as the clavicular portion of the deltoid, is 

 the true clavicular deltoid, whilst the muscle described in Orni- 

 thorhynchus as the clavicular portion of the P. major is in reality 

 the clavicular portion of the deltoid. We base our conclusions on 

 the following points : — Origin, insertion, relations, and nerve 

 supply ; the developmental not being available. 



