38 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XIV. 



Obturator externus. Origin from the side of the ascending ramus of 

 the ischium from the lower edge of the tuberosity to the symphysis and 

 thence on the side of the pubic ramus to a point nearly opposite the 

 anterior base of the marsupial bone. Insertion by a thick tendon in the 

 digital fossa and on the intertrochanteric ridge of the femur. It is a 

 broad thickened muscle lying at its origin entad of the adductors. Dor- 

 sally it meets the edge of the quadratus femoris. 



The obturator externus is said by Leche (p. 858) to be "nichts be- 

 merkenswerthes " in the Marsupialia, but Macalister (1870, p. 167) 

 states that it is "large and normal in Phascolomys and Sarcophilus, as 

 well as in Macro-pus giganteus, the Wallaby, Phalanger, and Opossum." 

 Thompson and Hillier (1905, p. 312) found it well developed inNotoryc- 

 tes. The so-called differentiation of the obturator, which Leche names 

 intermedius and reports only for Didelpkis and Philander is doubtless 

 not peculiar to these forms. It was not specially sought in Ccenolestes 

 and may have been overlooked and included as an integral part of the 

 externus. Whether it be called externus or intermedius, it is apparent 

 that it is not peculiar in C&nolestes. 



MUSCLES OF THE TAIL. 



All the usual tail muscles of the pubic cavity are present and distinct 

 but their muscular parts do not extend far beyond the base of the tail. 

 On removal of the skin and the underlying fascia, the tail appears almost 

 entirely encased in shining tendons from its base to its tip. On the dorsal 

 aspect the continuations of the back muscles proceed somewhat farther 

 caudad but these also soon become entirely tendinous. After all the 

 tendons have been removed, however, a series of thin muscles connecting 

 the vertebrae are exposed. These are short muscles, those next the 

 median line extending from the chevron bone of one vertebra to that of 

 the one succeeding; those laterad extend from the caudal transverse 

 process of one vertebra to the cephalic articular process of the second 

 succeeding vertebra, each muscle thus spanning a vertebra. 



Dorsally the tendons from the dorsal extensors cover the angles of 

 the tail, passing over the articular processes of the vertebrae, but in the 

 median line the short intervertebral tail muscles are exposed. 



Abductor caudae externus. Origin on the medial side of the iliac 

 crest and by tendinous connection with the lumbo- dorsal fascia. In- 

 sertion on the dorsal surfaces and tips of transverse processes of the 

 caudal vertebrae. This is a spindle-shaped muscle filling the great part 

 of the space between the transverse and the articular processes of the 

 anterior caudal vertebrae and passing out on the side of the tail where it 

 narrows and soon becomes wholly tendinous. 



