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



Thylacine it constitutes one unbroken muscular sheet. The cervical part is composed 

 in all of five slips from the transverse processes of the five posterior cervical vertebrae. 

 The costal origin differs in each case. In the Cuscus it is the most extensive, and 

 consists of eight digitations from the eight anterior ribs ; in the Phascogale it is formed 

 by seven digitations, and in the Thylacine by six digitations. In each animal it is 

 inserted into the entire length of the base of the scapula. 



Subclavius.— In the Cuscus (PI. II. fig. 4, s.c.) and Phascogale the subclavius presents 

 the ordinary attachments. In both it is very strongly developed, and arises by a pointed 

 tendinous origin from the cartilage of the first rib. Expanding in a fan-shaped manner, 

 it is inserted into the outer two-thirds of the upper sharp margin of the clavicle. In 

 neither case does the muscle extend beyond the outer end of the clavicle towards the 

 acromion process or supraspinatus fascia. 



In the Thylacine (PL I. fig. 5, s.c.) the connections of the subclavius are very different. 

 It is present in the form of a sterno-scapular band, which takes origin from the cartilage 

 of the first rib, and then proceeds outwards upon the superficial aspect of the axillary 

 vessels and nerves. Reaching the rudimentary clavicle, it sinks under cover of this bone 

 and its attached muscles, and sweeps over the tuberosities of the humerus like a strap. 

 It now changes its direction, and is carried upwards upon the supraspinatus, and is finally 

 inserted into the fascia covering that muscle. It has no direct attachment to the scapular 

 spine or to the outer end of the clavicle. 



According to Macalister, 1 the subclavius in the Wombat is inserted directly into the outer, 

 sixth of the clavicle, into the upper border of the acromion process, and into the scapular 

 spine. Professor Eolleston's description of the same muscle in this animal is somewhat 

 different. 2 He states that it is inserted into the outer end of the clavicle, and by means 

 of the fascia covering the supraspinatus into the whole length of the spine of the scapula. 

 In any case, from its having a clavicular attachment, the Wombat exhibits an intermediate 

 condition between the Cuscus and Phascogale on the one hand and the Thylacine on 

 the other. 



Cuvier and Laurillard figure (pi. clxxvi. fig. 1, h.hf) a subclavius muscle in Didelphys 

 cancrivora, which appears to have simdar attachments to those of the corresponding- 

 muscle in the Wombat. In the Macropus major (pi. cxcv. fig. 1, h), in the Macropus 

 minor (pi. clxxxi. fig. 1, h), and in the Phalangista cavifrons (pi. clxxix. fig. 3, h) the 

 same authorities figure the subclavius as it is found in the Cuscus and Phascogale. In 

 the Opossum Professor Haughton 3 states that the subclavius is inserted into " the under 

 surface of the outer third of the clavicle and the front of the acromion." 



I fully agree with Professor Macalister in his remark, that " we can scarcely regard 

 the sterno-scapular as anything but a variety of the subclavius." 



1 Loc. cit, p. 3. 



2 On the Homologies of Certain Muscles connected with the Shoulder-Joint, Trans. Linn Soc, vol. xxvi. p. 626 



3 On the Muscles of Marsupials, Proc. Roy. Irish Academy, vol. ix. p. 485. 



