852 DR. C. F. SONNTAG ON THE VISCERAL ANATOMY 



ursinus. Phascolarctos cinereus has the greatest number in the 

 posterior group, and the parathyroids may be included among 

 them. 



The on]y Marsupial with exoccipital processes touching the 

 deep aspect of the platysma is Phascolarctos cinereus. 



The MusGidar System. 



As considerable attention has already been paid to the muscles 

 of the Marsupialia, the present section is limited to some points 

 in the myology of the head and neck. 



The Platysma: — The origin, insertion, and relations are similar 

 in all Marsupials, but the characters difier considerably. In 

 JJendrolngn,s ursinus and Macropus rufus it is muscular in the 

 face but almost aponeurotic in the neck. In Perameles ohesula, 

 on the other hand, it is muscular and thick in the neck, but more 

 aponeurotic and firmer in the face; and it arises posteriorly fi-om 

 an equally strong and thick panniculus carnosus. In some parts 

 these muscles are nearly two millimetres thick, and it is difficult 

 to tell where the one ends and the other begins. The panniculus 

 is very thick over the pectoral region. Tliese conditions are 

 reversed in Ccenolestes obscurtrs, in which Osgood described a thin 

 panniculus and platysma. The platysma of Sarcopkilus harrisi 

 (text-fio\ 70 A) is muscular throughout, and its fibres cross at the 

 anterior extremity of the interramal space. Beneath it there lies 

 a stratum of more or less transverse fibres which fuse with it at 

 the sides of the neck. Although the latter cannot be traced to an 

 attachment in the face, they may correspond to the sterno-facialis 

 of some of the higher Mammalia, e. g. Octodon and the Carnivora. 

 The condition present here may indicate that the sterno-facialis 

 arises from the platysma by splitting. 



The Sterno-mastokl and Cleido-mastoid : — Carlsson (2) showed 

 that they are fused throughout the greater part of the neck in 

 JJendrolagas dorianus and Petrogale penicillata, but not in Tricho- 

 surus vulpecida ; and they are similarly fused in Dendrolaytis 

 ■ursinus. In a pouch specimen 'of Macropus giganteus they fuse 

 much farther forwards ; but the muscles of Peta/urus sciureus run 

 parallel to one another, and are only fused at their cranial 

 insertions. Osgood (9) records a similar condition in Ccenolestes 

 ohscurus, so it differs greatly from that in Perameles obesula, in 

 which the cleido-mastoid arises from the cephalo-humeral and fuses 

 Avith the cranial end of the sterno-mastoid. In Philander laniger, 

 Jletachiras opossum, and Didelphys the sterno-mastoid, cleido- 

 mastoid, and cleido-occipital form a group of three almost parallel 

 muscles traversing the neck obliquely from behind forwards. In 

 all species examined except D. azarce they had separate origins 

 from the clavicle ; but in that species the cleido-occipital was 

 implanted I5y tendon into the cleido-mastoid at its posterior 

 extremity. 



The posterior triangle of the neck is obliterated in Dendrolagus 

 ursinus- and Petrogale xanthopus, in Avhich the trapezius is in 



