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



The pectoralis major is inserted into the pectoral ridge of the humerus, whilst the 

 pectoralis minor finds attachment at a higher level into the great tuberosity of the 

 humerus, and also into the tendon of the supraspinatus. The two muscles therefore 

 cross each other as they pass towards their insertions. 



The pectoralis quartus is composed of two minute fleshy slips which arise from the 

 linea alba, and end by fusing with the under surface of the pectoralis major. 



A study of Cuvier and Laurillard's plates shows that the Phalangista cavifrons 

 (pi. clxxix. fig. 2,j,j 1 ,j 2 + j), the Macropus minor (pi. clxxxi. fig. \, j, j x ,p,j +), and 

 the Macropus major (pis. cxciii. and cxciv.) agree in almost every respect with the Cuscus 

 in the arrangement of the pectoral muscles. In the Wombat Professor Macalister 1 describes 

 the same four pectoral muscles ; in the Tasmanian Devil he states that the pectoralis 

 major is not segmented (i.e., there is no deep portion), and in this respect, therefore, it 

 corresponds with the Phascogale. In both these animals, however, the great pectoral 

 muscle receives fibres of origin from the clavicle. 



There is a diversity of opinion regarding the character of the pectoralis quartus. 

 Owen' 2 looks upon it as " a dismemberment of the pectoralis major." Humphrey and 

 Macalister x believe that it is in an " intermediate piece of the great superficial external 

 muscular sheet between the pectoralis major and latissimus dorsi." Its close connection 

 in many cases with the panniculus carnosus would almost seem to indicate that it is 

 merely a portion of this muscle. In the Cuscus, indeed, it appeared to be simply the 

 thickened lower margin of the panniculus, the connection between them was so intimate. 

 Scapular muscles. — In all the three specimens the supraspinatus is much more bulky 

 than the infraspinatus. This is most marked in the Phascogale in which it is fully 

 three times as large. In the Tkylacine it is nearly twice as large (PL I. figs. 4 and 5, s.s.) ; 

 in the Cuscus the disparity in size is not quite so great. 



A teres minor, distinct from the infraspinatus, is present in the Thylacine (PI. I. fig. 

 4, t.m 2 .) and Cuscus. In both cases this muscle is supplied by a small twig from the 

 circumflex nerve. It arises from a small portion of the axfllary border of the scapula 

 close to the glenoid cavity, and is inserted into the humerus upon its outer and posterior 

 aspect immediately below the great tuberosity. In the Phascogale the teres minor is 

 absent, and no twigs from the circumflex nerve could be traced to the portion of the 

 infraspinatus which might be supposed to represent it. 



The teres major is well developed in each of the three specimens. It has a very 

 slight origin from the dorsum of the scapula at the posterior angle of the bone. Its main 

 origin is from the axillary border of the scapula in its upper two-thirds. Here it is 

 intimately connected with the posterior border of the subscapulars by means of an 

 intermuscular septum, which gives fibres to both. In the Cuscus (PI. II. fig. 4, t.m.) and 

 Phascogale it receives a slip from the latissimus dorsi, and is then inserted into the inner 



1 Loc. cit., p. 3. 3 Anatomy of Vertebrates, vol. iii. p. 12. 



