MAY, 1921. AMERICAN MARSUPIAL, CJSNOLESTES OSGOOD. 23 



ginning in the middorsal line near the origin of the latissimus dorsi 

 (and immediately overlying and parallel to it), a thin sheet of converging 

 fibers runs forward and downward to the axilla. Similar converging 

 fibers from the mid-thoracic region and from the abdomen join those 

 from above and unite to form a single muscle which enters the axillary 

 region dorso-laterally just below the latissimus dorsi and ventrally 

 parallels the outer edge of the pectoralis major. It makes a turn on itself 

 and inserts as usual on the proximal two thirds of the inner edge of the 

 deltoid ridge of the humerus. The abdominal part of this muscle is 

 somewhat differentiated into a humero-dbdominalis or xiphi-humeralis 

 (pectoralis quartus). This begins to be fleshy on the middle of the abdo- 

 men and anteriorly divides to pass on either side of the pectoralis and 

 parallel to it. On entering the axilla it becomes fused with the cutaneus 

 maximus and has a common insertion with it. It has similar relations in 

 most marsupials. 



Cervico-auricularis. This is a thin paired sheet arising from the oc- 

 ciput and the nuchal crest for a distance of about 10 mm. or to the 

 fatty deposit in the interscapular space. It is inserted on the cartilage of 

 the back of the ear and into the ental surface of the superficial fascia be- 

 low the ear for some 8 mm. lengthwise of the side of the neck. Dorsally 

 it leaves the base of the ear for a short distance and attaches to the 

 ectal surface of the muscle which elsewhere underlies it and which is here 

 called the auriculo-occipitalis. 



Auriculo-occipitalis. Arises from the nuchal crest entad of the 

 cervico-auricularis, the anterior limit of its origin being even with that 

 of the ceroico-auricularis and the posterior slightly cephalad of it. Its 

 two halves separate on the occiput and diverge over the parieto-squa- 

 mosal region to overly the caudal part of the temporal muscle. Directly 

 above the ear, it passes into the ental surface of the superficial fascia or 

 panniculus and thence around the anterior base of the ear the two are 

 inseparable. 



Dorso-cuticularis. A long slender muscle arising on the side of the 

 twelfth thoracic vertebra and running forward along the boundary be- 

 tween the latissimus dorsi and the trapezius to the side of the scapula 

 where it widens slightly and inserts on the ental surface of the thin outer 

 sheet of the panniculus. Its width at its insertion is 1.5 mm. I have 

 been unable to find any trace of this muscle in Didelphis nor any record 

 of its occurrence in any other marsupial. Its form and relations are 

 almost exactly as in the Insectivora where it is of frequent occurrence. 

 Somewhat similar muscles are found also in certain edentates. (See 

 Plate III.) 



