10 THE VOYAGE OF H.M.S. CHALLENGER. 



origin to the same muscle in discus. It is inserted into the outer aspect of the shaft of 

 the humerus about an inch below the great tuberosity, and at a higher level than the 

 clavicular deltoid. It receives no fibres from the trapezius. The clavicular deltoid is 

 composed of fibres derived from three distinct sources. In great part it is formed by 

 fibres which come from the trapezius and the cleido-mastoid muscle, but it also obtains 

 some which spring directly from the lower border of the rudimentary clavicle. Thus consti- 

 tuted it is inserted into a ridge upon the antero-external aspect of the shaft of the humerus 

 about its middle, where it is partially fused with the insertion of the pectoralis major. 



According to Macalister 1 the deltoid in the Wombat is double, whilst in the Tasmanian 

 Devil it is triple as in the Phascogale. The same authority states that the muscle is 

 "undivided" in the Giant Kangaroo, in Macropus bennettii, the Phalanger, and the 

 Virginian Opossum. In the Koala 2 it is composed of two parts — clavicular and 

 scapular. The above facts might lead us to question the general applicability of the 

 assertion made by Owen in his great work upon the Comparative Anatomy of Vertebrates 

 that " in claviculate Marsupials the deltoid . . . consists of three fasciculi." 



Cephalo-humeral muscle. — We are now in a position to understand the constitution of 

 the composite muscle to which this name is applied. In the Cuscus it consists of that 

 portion of the trapezius which, in man, is inserted into the acromion and clavicle united 

 with the acromial and clavicular parts of the deltoid. In the Thylacine and Phascogale, 

 on the other hand, the acromial deltoid is not a constituent. In the former (PL I. fig. 4, 

 c.h.) it is composed of the cleido-mastoid, the anterior fibres of the trapezius, and the 

 clavicular deltoid, in the latter it is formed by the anterior fibres of the trapezius and the 

 clavicular deltoid. 



Coraco-brachialis. — Professor John Wood has taught us, in his well-known paper 

 upon Muscular Variations, 3 to look upon the typical coraco-brachialis as being a 

 muscle with a triple constitution. The animals in question afford a beautiful example of 

 this. In each the coraco-brachialis brevis is present, and in Thylacinus it constitutes the 

 sole representative of the muscle, which in this respect therefore resembles the carnivora. 

 It springs from the coracoid processes, in common with the coracoid portion of the biceps. 

 and spreading out in a fan-shaped manner, passes downwards over the insertion of the 

 subscapularis to find attachment to the shaft of the humerus immediately above the 

 insertion of the teres major. It is a short thick fleshy muscle. 



In addition to the short muscle, the Phascogale possesses a coraco-brachiahs medius — 

 a very slender fascicidus which is inserted into the middle of the inner aspect of the shaft 

 of the humerus, whilst in the Cuscus we find a coraco-brachialis longus (PL II. fig. 4, 

 c.b.l.) inserted into the bridge of bone which walls in the supra-con dyloid foramen of the 

 humerus. 



1 Loc. cit, p. 3. 2 Young, Muscular Anatomy of Koala, Journal of Anatomy and Physiology, vol. xvi. 



3 Journal of Anatomy and Physiology, vol. i. 



