22 
be formed from factors of the pectoralis major which, or some of which, 
represent the epicoraco-humeral of Urodelans, Reptiles, and Mono- 
tremes.” And Mivart himself regards the subclavius as r2presented in 
Echidna by “a small and thin muscle which arises from the anterior 
border of the first rib for the greater part of its length, and which is 
inserted into the coracoid immediately behind (or rather above) the 
origin of the coracobrachialis.’’* 
This “ costo-coracoid” muscle in Echidna is described and figured by 
Westling. + 
Iam indebted to Dr. McKay for most of the following particulars 
regarding the corresponding conditions in Ornithorhynchus.{ A fairly- 
strong costo-coracoid muscle is present, with similar attachments to 
those in Kchidna given above, from Mivart. Its fibres converge to a 
tendinous insertion into the posterior tip of the coracoid. This muscle 
must, I imagine, correspond to the ‘‘pectoralis minor” referred to by 
Owen$ as “inserted into the coracoid,’ or less probably to his 
“ subclavius,”’ which he describes as “ also inserted into the coracoid.” 
While, then, the costo-coracoid muscle of Ornithorhynchus is either 
Owen’s lesser pectoral or his subclavius, the other of these must find 
its homologue in a muscle called by Westling in Echidna “sterno- 
coracoid,|| but which neither in that animal nor in the Ornithorhynchus 
is attached to the coracoid, though it is in close relation to that bone. 
Thus in Ornithorhynchus it arises from the anterior border of the first 
costal arch just mesiad of, and close to, the costo-coracoideus ; and 
it also arises from the dorsal, or deep, aspects of both the interclavicle 
(slightly) and the presternum. It is inserted into the anterior half of 
the dorsal or deep surface of the epicoracoid in close relation to (mesiad 
of) the origin of the “ epicoraco-brachialis.””’ A somewhat more appro- 
priate, if more cumbrous, name for this muscle is M. sterno-costo- 
epicoracoidenus. aay 
Both of these muscles (Mm. costo-coracoideus and sterno-epicoracoi- 
deus) I take to represent the ordinary mammalian subclavius, for not 
only are the two muscles in such close relation, possessing analogous 
attachments, but their innervation is from a common source, viz., a 
branch of the brachial plexus (ventral aspect) homologous to the 
nervus thoracicus inferior of Fiirbinger in Saurians,{ and probably 
to the “‘ nerve to the subclavius”’ of mammals. 
In Echidna Dr. McKay finds this nerve giving a branch to the 
phrenic, as the nerve to the subclavius occasionally does in man. 
Their segmentation as distinct muscles is doubtless correlated with 
the partially independent mobility of coracoid and epicoracoid. 
The marked divergence of type from the ordinary mammalian sub- 
clavius is dependent upon the high development of the coracoids, 
causing interruption of the fibres, and thus arresting them in their 
passage towards clavicle and scapula. 
In Chlamydophorus** the subclavius is large, and has a wide origin 
from the broad sternal segment of the first costal arch. It passes 
beneath clavicle, and is inserted into the coracoid process, the acromion 
and the acromial end of the clavicle very slightly or not at all (Hyrtl).t+ 
*xxxix., page 382. t+lxil., page 14, and Taf. ii, fig. 6 c.c. {lxxvil. 
§xlv., page6. || lxii., page 15, and Taf. ii., fig. 6 st. c. 4] xili., page 709-11. 
** xxvil., page 241. ti xxiv., page 32. 
