OF DIDELPHYS VIRGINIANA. HI 



and curves around the shoulder to the middle of the clavicle, thus determining the contour 

 of the side of the neck, as in man. It arises fleshy, or by a very short aponeurosis in some 

 places, from the whole of the occipital ci'est, ligamentum nuchae and spines and interspinous 

 ligaments of all the cervical and dorsal vertebne, overlying the rhomboideus and greater part 

 of the latissimus. The upper fibres pass downward, outward and forward ; the middle ones 

 directly forward ; the lower ones obliquely upward and forward ; converging, in this manner, 

 into a broad, flat tendon, that passes along and is attached to the scapular spine, acromion, 

 and distal half of the clavicle. The aponeurosis plays freely over the root of the scapular 

 spine ; elsewhere it is intimately adherent to the fascial investment of the two spinati muscles, 

 the deltoid and great pectoral. The muscular fibres themselves are not, however, continued 

 directly into the pectoralis major, as is said to be the case with some marsupials (e. g., 

 Perameles lag oils : teste Owen, C. Anat. in., p. 11). The portion of the muscle that is 

 inserted into the clavicle often, perhaps usually, forms a separate fasciculus that lies along 

 the anterior cervical border, and is only united to the rest of the muscle near the 

 side of the occiput. The part that lies over the protuberance of the shoulder is always 

 extremely thin, and discontinuity of the plane at this point produces this clavicular slip. 



Rhomhoideus. — (Fig. 28, d.) Thei-e is no distinction of rhomboideus major and minor; 

 the single muscle forms a continuous thin plane, overlaid by the trapezius, arising from the 

 occipital crest and nuchal ligament next to the origin of the trapezius, and from the verte- 

 bral spines and interspaces as for down as the commencement of the latissimus, which is 

 at a point just opposite the middle of the trapezius and the extremity of the scapula. It 

 is inserted into the posterior border of the latter, fleshy, or with a very short aponeurosis, 

 for nearly an inch. It draws the shoulder lalade backward and upward. 



Serratus magnus (fig. 28, e), and Levator anguli scapulce (fig. 28,/). — The very large 

 triangular plane of fibres that converges to be inserted into the posterior border of the 

 scapula cannot be separated into two muscles except by arbitrary use of the knife. The 

 upper fibres elevate, and the lower depress, the extremity of the bone ; the whole acting 

 together draw the shoulder directly forward upon the thorax. This arrangement, in all 

 probability, relates to the animal's hugging of objects when climbing. The cervical or ver- 

 tebral portion of the muscle, which is the levator, arises in slips from the posterior part of 

 the transverse process of the four or five lower cervical vertebme, more or less blended with 

 the posterior scalenus. The thoracic or costal portion, which is the serratus, arises from the 

 first eight or nine ribs, by as many fleshy digitations ; beginning at the middle of the first 

 rib, curving gradually towards the back-bone on successive ribs from above downward. 

 The four or five lower slips are most distinct from each other, and interdigitate with the 

 obliquus abdominis externus ; they pass obliquely upward and backward ; the upper ones 

 directly backward ; the latter are overlaid by the scalenus as low down as the fourth rib. 



Omo-hyoideus. — (Fig- 28, i.) A broad, flat ribbon-muscle, arising fleshy from the side 

 of the hyoid bone between the genio- and thyro-hyoid, and running downward a little way 

 upon the sterno-thyroid ; then curving away from the trachea, passing obliquely across the 

 neck, underneath the sterno- and cleido-mastoid, above and beyond the shoulder to gain the 

 posterior superior angle of the scapula, where it is inserted by a short, flat tendon, beside 

 the insertion of the atlanto-scapularis. The extension of this muscle to the further end of 

 the scapula at once augments its power, and causes it to become virtually a third elevator 

 of the scapular angle. The omo-hyoid is a single simple band, with one curve in its whole 



