870 DR. C. F. SONNTAG ON THE MYOLOGY 



In Phascolomys, on the other hand, most of the fibres cross the 

 clavicle and fuse witli the clavicular deltoid ; and some fuse v^^ith 

 the cleido-mastoid. In Phalanger the conditions are intermediate. 

 The scapular insertion is, however, similar in all. And in no case 

 is there a tendinous intersection where the fibres cross the 

 clavicle. The fusion of the trapezius and clavicular deltoid is a 

 persistence of the primitive lamination, and is best marked in 

 Phascolomys. 



Phomboideus: — In all forms it is an indivisible sheet whose 

 origin extends from the occiput anteriorly to the thoracic region 

 posteriorly, and it thickens from befoi'e backwards. It reaches 

 the fifth dorsal spine in Phascolomys, but stops at the third 

 in Phascolarctos, Phalanger, and Pseudochirus. As the rhom- 

 boideus shows no division in any of these animals they all exhibit 

 a persistence of the primitive condition of the muscle. 



Latissimus Dorsi : — This muscle arises from a variable number 

 of posterior thoracic spines and the lumbar fascia, but there are 

 neither iliac nor scapular origins. Costal slips may exist. The 

 following origins were present in my specimens : — 



Phascolarctos : spines 4-10 ; no costal origin. 

 Phalanger : sj)ines 4-12 ; slip from last rib. 

 Pseudochirus : spines 4-12 ; no costal origin. 

 Phascolomys : spines 5-15 ; slips from lower six ribs. 



The insertion of the latissimus is very similar in all, and it is 

 intimately connected to the teres major and dorso-epitrochlearis. 



Levator Anguli Scapulce : — Young (14) states that it arises from 

 the front of the latei'al mass of the atlas along with the first slip 

 of the serratus magnus in Phascolarctos ; but he does not mention 

 whether it is fused with the omo-atlantic. It is inserted into 

 the scapular spine. In Phascolomys I observed it arising in 

 company with the omo-atlantic from the caudal border of the 

 lateral mass (text-fig. 36 A). And it is closely connected to the 

 upper part of the seri-atus magnus. It is attached to the root of 

 the spine of the scapula. In Phalanger (text-fig. 37) it arises in 

 common with the omo-atlantic, bvit is separate from the serratus 

 magnus. It is inserted into the dorsal surface of the scapula in 

 the anterior part of the supraspinous fossa. In Pseudochirus, on 

 the other hand, it is inseparable from the serratus magnus, and its 

 insertion never reaches the spine of the sc!::pula. It is, therefore, 

 evident that Phascolomys and Phascolarctos differ from the 

 Phalangers in the insertion of the levator scapulse. So the 

 conditions of the levator scapulae and serratus magnus are degrees 

 of persistence of primitive lamination. 



Omo-atlantic (text-figs. 36 cfe 37) : — In Phascolomys and Phasco- 

 larctos it runs, widening as it goes, from the lateral mass of the 

 atlas to the outer part of the spine of the scapula. And the 

 lateral fibres cover the dorsal part of the shoulder joint. In 

 Phalanger and Pseudochirus it divides into two parts — a broad 

 mesial and a narrow lateral slip—and these are attached to the 



