15 
This arrangement of the fibres of the deltoid series closely resembles 
that figured jby Cuvier & Laurillard in Phalangista,* and described in 
P. vulpina by MacCormick.t It is thus ot the bipartite variety, the 
scapular deltoid not being segmented into acromial and spinous 
portions. 
The muscle is unsegmented in the Giant Kangaroo (Macalister and 
Cuvier & Laurillard) Macropus minor (C. & L.), Macropus Bennettii, 
and Didelphys (Macalister).{ Itis bipartite in Cuscus and Thylacinus,$ 
as well as in the Vulpine Phalanger, as already mentioned; also in the 
Wombat,|| and in Koala according to Young,! though according to 
Macalister** it consists of “three parts inseparably united” in the 
latter animal. 
It is tripartite in Phascogale,¢ + and in Dasyurus viverrinus.t{ In Sarco- 
philusS§ the spinous and acromial portions of the scapular deltoid are 
separate, but there is “no clavicular deltoid separate from the outer 
fibres of the acromial portion.” 
In Perameles an accessory slip from the inferior costa of the scapula 
is present according to Owen.|(|| 
The deltoid in OrnithorhynchusT1 is generally regarded as single and 
scapular, though}|Owen*** follows Meckeltt7{ in regarding as an anterior 
part of the deltoid that deep ventral muscle which Mivart{{{ has named 
“ epicoracohumeral”’ in Echidna. Cuvier and Laurillard figure the latter 
muscle$$$ as a middle or lesser pectoral. 
In Echidna, Mivart|||||| describes and figures a double deltoid; one 
portion is scapular, and corresponds to that in Ornithorhynchus, while 
the other is claviculo-acromial, and corresponds in position and at- 
tachments to a muscular sector, which seems to constitute the most 
anterior division of the pectoralis major in Orinithorhynchus. 
Westling,111 in remarking upon this correspondence, raises the ques- 
tion for future decision whether in Ornithorhynchus we have a fusion of 
originally distinct muscles, or whether the condition in this animal is 
primary, the anterior part of the deltoid in Hchidna having arisen as 
a secondary differentiation from the pectoralis major. 
Westling states that the two muscles are certainly homologous, cor- 
responding in origin, position, and innervation. Working in this 
laboratory, my friend and former pupil, Dr. W. J. McKay, has satisfied 
himself of this homology, and is strongly inclined to the belief that 
the sector in question in Ornithorhynchus in reality belongs to the del- 
toid system, and not to the pectoral. He finds that it corresponds 
accurately in postion and attachments to the “anterior deltoid”’ in 
Echidna, and as in the latter animal it splits at its insertion to enclose, 
or rather it is folded round, the tendinous insertion of the posterior 
deltoid. Again, he confirms Westling’s statement in reference to the 
innervation of the muscle. As in Hehidna, so in Ornithorhynchus, it is 
supplied exclusively by the “nervus axillaris,” which also supplies the 
posterior deltoid in both animals. The anterior thoracic nerves which 
Ova tel 177, fig) 2. ane Pl horn lai pete, pace, 115): tein, 
page 159. §iv. || xxix., page 159. ‘I 1xxii., page 226. ** xxviii., page 
130. Tfriv., page 9. }}xxxvi., pagelldS. §§ xxix., 159. ||| xlv., page 11. 
I xxvi., page 791, and vi. Pl., 265, fig. 2. ***xlv., page 6. ttt xxxvili., 
page 26. {it xxxix., page 384. §§§ vi. Pl., 266, fig. 2. |\II|| xxxix., page 
o84, Pl. 52, fig. 2. WI lxii., page 17. 
