OF DIDELPIIYS VIRGINIANA. 113 



is inserted into the greater tuberosity of the Immerus, and upper part of the outer lip 

 of the bicipital groove. It abducts and anteducts the humerus, at the same time rotating 

 the bone inward. 



PectoraUs major, its third division. — Of large size, and the longest of the three, though 

 thin and flat. It arises, in apposition with its fellow, from the linea alba for an inch or two 

 below the xiphoid, narrowing rather suddenly to become a thin, slender ribbon that pro- 

 ceeds in a straight line obliquely forward and outward to be inserted, by a narrow, thin 

 aponeurotic tendon, into the upper part of the outer edge of the bicipital groove close to 

 the humeral tuberosity. Its insertion and action are nearly the same as those of the 

 middle pectoral ; it continues and augments the force of the latter. With its fellow, it 

 forms a large V across the ventral aspect of the body, lying chiefly upon the thoracic pro- 

 longation of the rectus, and the scalenus, both of which it crosses obliquely. Its presence 

 is of a part with the general preponderance of muscles that aid the flexion of the body and 

 limbs over those that extend ; it probably relates to the manipulation of the abdominal 

 pouch and genitalia, in much the same way that has gained for the latissimus dorsi, in 

 anthropotomy, the pseudonym of " scalptor ani." ^ 



Latissimus dorsi. — (Fig. 28, h.) The great muscle of the back extends from the ter- 

 mination of the rhomboideus to the 3d and 4th lumbar vertebra. The aponeurosis of origin 

 is nsirrowest above, where fleshy fibres reach nearly to the median line, and broadest over 

 the loins ; this tendinous lamina and the fleshy part of the muscle are both very thin. 

 The upper border of the muscle is directly transverse ; at first in relation with the rhom- 

 boideus, afterward with the teres. The lower or exterior border is very long ; it proceeds 

 obliquely forward and outward, presenting the usual twist by means of which it becomes 

 the upper border of the tendon of insertion. The latter is an inch or more long, but 

 scarcely a fourth of an inch wide ; it is implanted in the humerus about an inch below the 

 head of the bone, on the posterior or inner border of the bicipital groove, alongside, or a 

 little above, the insertion of the teres. 



Dermo-hrachialis. {Fannicidus carnosus.) — The large cutaneous body-muscle envel- 

 opes nearly all the back, side, and belly, with very extensive origin from the skin of the 

 parts, meeting its fellow along the middle line of the belly, but separated, in most of its 

 extent, over the back. It is properly a part of the panniculus of the head and neck already 



^The pectoral muscle of another (a non-c-laviculato) mar- anterior faseieuli, and arc inserted into tlie coracoid process, 



supial, the Perameles lagolh, is thus described by Owen. thus representing the pectoralis minor. Beneath this latter 



(Comp. Anat. and Phys. iii. p. 12): portion of the pectoral, a long and slender muscle passes to 



'• The pectoralis major is, as usual in the marsupial and be inserted into the anterior part of the tuberosity of the 

 many higher cpiadrupeds, a complicated muscle; it consists humerus; this may likewise be regarded as a dismemberment 

 of an anterior or superficial and a posterior or deeper ])or- of the pectoralis major, but it arises from the fascia of the 

 tion; the anterior portion receives the strip before mentioned rectus abdominis, below the cartilages of the lower ribs." 

 from the trapezius, there being no clavicle or clavicular The three pectorals of marsupials recall the three of birds, 

 ossicle interposed in the Perameles; its fibres converge, in- and tlie suggestion is strengthened by the avian affinities 

 creasing in thickness as they diminish in breadth, and are that these animals and the iMonotremes show. One might 

 inserted into the anterior and outer part of the strongly de- well be excused for taking the hint, at first blush of the 

 veloi)ed pectoral ridge. The second and main portion of the question; but nevertheless it seems fallacious, the balance of 

 pectoralis arises from tlie whole extent of the sternum; its evidence being decidedly the other way. If the three pec- 

 fibres are twisted obrKjuely across each other as they con- torals are really dismemberments of one, it is more than 

 verge to be inserted into the inner part of the pectoral ridge; probable that what I have called " sterno-costalis " is really 

 some of the internal and posterior fibres of this portion of the true pectoralis minor, 

 the twisted pectoral pass obli(iuely upward and behind the 



MEMOIRS BOST. 800. SAT. HIST. VOI-. II. 29 



