TRANSACTIONS OF THE SECTIONS. 109 



tlio fibres which take origin from the spine of the scapula. The humeral portion 

 of the trapezius joins the clavicular part, and the muscle has the same insertion as 

 in the Cuscus. 



In the Thylaoine the deltoid is in two parts, a scapular and a clavicular, and 

 these are separate from each other, both at their origin and insertion. The scapu- 

 lar deltoid is much the more extensive of the two. Its origin is the same as in 

 the Ciischs. It is inserted into the outer aspect of the humerus, distinct from, and 

 at a higher level than, the clavicular deltoid. The clavicular deltoid derives iibres 

 from three distinct sources. The chief proportion is derived from the trapezius 

 and cleido-mastoid muscle, but it also receives some which spring directly from 

 the rudimentary clavicle. This portion of the deltoid is inserted into the outer 

 aspect of the shaft of the humerus at a lower level than the preceding. 



We are now in a position to understand the constitution of the compound muscle 

 known in comparative anatomy as the cephalo-humeral muscle. We have already 

 studied its component parts. 



In the Cuschs it consists of that portion of the trapezius which in man is inserted 

 into the acromion and clavicle, joined with the acromial and clavicular parts of the 

 deltoid. In the Thylacine and Phaseoyale, on the other hand, the acromial deltoid 

 is not a constituent. In the former it is composed of the cleido-mastoid, the 

 anterior fibres of the trapezius, and the clavicular deltoid ; in the latter by the 

 anterior fibres of the trapezius and the clavicular deltoid. 



Teres minor. — This muscle is very short, but present in them all, and quite dis- 

 tinct from the infraspinatus. 



Triceps. — In the Thylacine the origin of the long head is remarkable for its great 

 extent. This portion of the muscle arises from nearly the whole length of the 

 axillary border of the scapula. But all the fibres springing from this do not reach 

 down to the olecranon. They consist of two sets : — (1) A set arising from the 

 scapula, close to the glenoid cavity, and running down in the form of a thick round 

 fleshy muscle, which, as it approaches the elbow, blends with the other two heads 

 of the triceps. (2) A set springing from the axillary border of the scapula, posterior 

 to this, which constitutes a thin fleshy mass composed of short fibres. These short 

 fibres curve forward, and are lost amongst those which spring from the scapula 

 close to the glenoid cavity. 



Coraco-brachialis. — Professor Wood, of King's College, London, in his very able 

 paper upon " Muscular Variation " (Journ. of Anat. and Phys. vol. i.), has taught 

 us to look upon the typical coraco-brachialis as being a muscle with a triple con- 

 stitution. The animals in question afford a beautiful example of this. 



In all three the coraco-brachialis superior is found, whilst in addition the median 

 variety is present in the Phaseoyale, and the long variety in the Citscus. 



Latissimus dor si. — In the Cuscus and Phascogale the insertion of this muscle is 

 the same ; in the Thylacine it is somewhat different. In all it is more or less con- 

 nected with that of the teres major. 



In the Cuscus and Phaseoyale the latissimus, as it approaches the humerus, 

 divides into two parts. Of these the upper and smaller slip, which corresponds to 

 the superior margin of the muscle, passes behind the other part and, joining the 

 lower margin of the teres major, is inserted into the inner lip of the bicipital 

 groove. The lower and main portion of the muscle ends in a strong tendinous band, 

 which is attached to the bottom of the bicipital groove, separated by a wide 

 interval from the insertion of the teres major. 



In the Thylacine the teres major and latissimus dorsi have a common insertion 

 into the humerus, and chiefly through the medium of a strong tendinous band, 

 which arches backwards from the bottom of the bicipital groove, where it is firmly 

 fixed to the humerus. This band is twisted upon itself so that its lower margin 

 has a round and cord-like appearance. Into its anterior half are inserted tho 

 greater proportion of the fibres of the -teres major, only a small portion of this 

 muscle being directly attached to the bone, and into its posterior half the latissimus 

 dorsi is inserted. 



The dorsi cpitrochlear muscle is present in them all. 



Pectoral muscles. — These muscles have a very complicated arrangement. 



Cuscus, — In this animal we have four distinct factors : — (1) A large superficial 



