8 ANATOMY OF VERTEBRATES. 



40, peroneus brevis, 41, extensor digitorum profundus, 42, extensor 

 digitorum sublimis, 43, a portion of the same muscle corresponding 

 with the indicator of the fore leg, and 44, extensor digiti quinti 

 accessorius. 



§ 194. Muscles of Marsupialia. — The most common posture 

 of the Kangaroo is often termed the ( erect ; ' yet the conditions of 

 this posture are very different from those in the human subject. 

 The trunk, instead of resting upright on two nearly vertical pillars, 

 is here swung upon the femora as upon two springs, which 

 descend from the knee-joints obliquely backward to their points 

 of attachment at the pelvis ; and the trunk is propped up behind 

 by the long and powerful tail, vol. ii., fig. 211. 



In Man the massive and expanded muscles which find their 

 attachment in the broad bones of the pelvis, especially at the 

 posterior part, are the chief powers in maintaining the erect 

 posture. But in the Kangaroo the glutcei offer no corresponding 

 predominance of size ; the narrow prismatic ilia could not, in fact, 

 afford them the requisite extent of fixed attachment. 



The chief modifications of the muscular system in relation to 

 the erect position of the trunk in the Kangaroo are met with on 

 the anterior part of the base of the spinal column. The psoas. 

 parvcB, for example, present proportions the reverse of those 

 that suggested their name in human anatomy. They form two 

 thick, long, rounded masses, which take their origin, fleshy, from 

 the sides of the bodies and base of the diapophyses of the lower 

 dorsal and all the six lumbar vertebrae, and from the extremities 

 of the three last ribs ; the fibres converge penniformwise to a 

 strong, round, middle tendon, inserted in the well-marked tubercle 

 or spine of the pubis, already noticed. 



The abdominal muscles include a pyramidalis as remarkably 

 developed as in the Monotremes. In the Phalanger, fig. 4, 

 the external oblique, besides the usual origin by digitations 

 from the ribs, also arises from the fascia lumborum; it is in- 

 serted fleshy into the summit of the marsupial bone, a, over 

 which its strong inner tendon is spread : the external oblique 

 becomes aponeurotic at a line continued from the marsupial 

 bone outward, with a gentle curve, toward the anterior ex- 

 tremity of the ilium; and in the opposite direction, or inward, 

 the carneous fibres of the external oblique terminate in an 

 aponeurosis along a line parallel with the oblique outer margin 

 of the pyramidalis ; the fascia continued from the latter boundary 

 of the fleshy fibres passes over, or dermad of, that muscle, 

 and meets its fellow at the linea alba ; it is homologous 



