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



In the Guscus the acromio-trachelien consists of two distinct fleshy bands — a small 

 superior band and a larger inferior band. These may appropriately be called the acromio- 

 trachelien superior and acromio-trachelien inferior. The former arises by two slips from 

 the transverse processes of the atlas and axis vertebrae, whilst the latter takes origin from 

 the transverse process of the atlas alone. Narrow and rounded towards their origin they 

 wind round the lower margin of the splenitis, and then diverging from each other as they 

 proceed backwards they expand into two thin muscular bands. Near the scapula they 

 coalesce, and are inserted into the whole length of the scapular spine, and also into the 

 posterior margin of the acromion process. 



In the Phascogale the arrangement is very similar ; still there are certain essential 

 points of difference. Thus both fleshy bands arise from the atlas alone, they remain 

 distinct throughout their entire extent, and, lastly, the acromio-trachelien superior, as it 

 approaches the scapula, fuses by its upper margin with the rhomboideus. 



In the Thylacine the single acromio-trachelien arises from the lower aspect of the 

 transverse process of the atlas, and, expanding as it passes backwards, is inserted into the 

 lower half of the scapular spine and into the posterior border of the acromion process 

 (PL I. fig. 5, a.t.). 



Cuvier and Laurillard (pi. clxxxviii.) figure a double acromio-trachelien in the 

 Macropus major, the two parts of which are very distinct, and inserted at a considerable 

 distance from each other. 



Cleido-occipital. — This muscle is found in Cuscus and Phascogale, but it is absent in 

 the Thylacine. 



In the Cuscus (PI. II. fig. 1, c.o.) it is a very narrow slip of muscle, and being closely 

 applied to the upper margin of the cleido-mastoid, it is not at first apparent. Posteriorly 

 it is attached to the sternal end of the clavicle, anteriorly it is inserted into the occipital 

 ridge upon the same plane as the trapezius and sterno-mastoid. 



In the Phascogale the cleido-occipital is a well-marked muscle, which is clearly 

 mapped off from the cleido-mastoid throughout its whole length. Its attachments are 

 the same as in the case of the Cuscus, but as it approaches the occiput it fuses with the 

 anterior margin of the trapezius. 



In the AVombat and Tasmanian Devil the cleido-occipital is absent ; at least Macalister 1 

 makes no mention of it in either case. In Cuvier and Laurillard's plates it is figured in 

 the Didelphys cancrivora (pi. clxxvi. fig. 1) and in the Macropus minor (pi. clxxxi. 

 fig. 1), but not in the Phalangista cavifrons (pi. clxxix. fig. 1). 



Cleido-mastoid. — In Cuscus and Phascogale this muscle arises from the sternal end 

 of the clavicle, in close proximity to the origin of the cleido-occipital. As it proceeds 

 forwards it sinks under cover of the sterno-mastoid to gain its insertion into the mastoid 

 process. 



1 Loc. cit., p. 3. 



