14 
In Ornithorhynchus the sterno-mastoid is double, one portion being 
placed beneath the other.* Neither cleido-mastoid nor cleido-occipital 
are segmented off from the sterno-mastoid-trapezius system in either 
of the monotreme forms.t In Echidna the sterno-mastoid has an ex- 
tensive origin from the ventral face of the median bar of the inter- 
clavicle, the presternum, and a large part of the meso-sternum. Its 
origin covers part of the origin of the pectoralis major. The origin, as 
I have found it, is thus more extensive than Mivart describes it; nor 
did I find it so narrow as he did. 
A cleido-mastoid is present in Chlamydophorus,{ Tatusia,t Dasypus,§$ 
Orycteropus,|| and amongst other Edentata, though: it is ot invariably 
present, while the cleido-occipital is frequently absent in this order, 
though present in Chlamydophorus and some others. 
Both sterno- and cleido-mastoids are usually present in Rodentia 
Insectivora and Caruvora, though the segmentation of the cleido-mas- 
toid from the sterno-mastoid is frequently incomplete. A cleido-occi- 
pital, too, is generally developed, but its relations are often modified 
by the partial or complete suppression of the clavicle, when it may 
enter, with the clavicular deltoid, into the formation of a cephalo- 
humeral muscle. It is very frequently, wholly or partially, fused with 
the cleido-mastoid, or in some forms with trapezius. 
I cannot find any instance in these orders of entire absence of both 
cleido-mastoid and cleido-occipital. 
M. deltoideus (figs. 1-5, d.t., ¢.d.t., ¢.d., and s.d.) consists of two 
distinct sectors, in addition to the delto-trapezius already 
described (trapezio-deltoid). The latter occupies a position inter- 
mediate between the other two in its course distally towards the 
humerus, and in its course it crosses and covers the insertion of 
the subclavius into the mesial border of the ‘ meso-scapular seg- 
ment.” 
The clavicular portion of the deltoid (JZ. cleido-deltordeus ), figs. 
3 and 7, c.d.) is comparatively small, and arises from the outer 
or lateral third of the clavicle, and thus corresponds to the inser- 
tion of the cleido-trapezius. It covers part of the subclavius 
muscle. 
The scapular portion of the deltoid (spzno- or acromio-deltoid 
figs. 1-5, s.d.) takes origin from the outer or lateral borders of 
the acromion and meso-scapular segment, and from the entire 
length of the post-axial lip of the true scapular spine (meso- 
scapula), the posterior fibres lying in the sulcus between the 
scapular spine and the broad scapular head of the triceps muscle 
(fig. 2, tr.). This part of the muscle is crossed by the ribbon- 
like spino-trapezius. 
All three sectors of the muscle (including the delto-trapezius) 
are inserted into the proximal tubercle and mesial border of the 
elongated delto-pectoral tuberosity of the humeral shaft. 
*xlv., page 5. +xxxix., ipage 38]. ‘tt xxvii., page 232. §xiv., page 
527. ||xv., page 571. ‘I xxvii., page 232. 
