110 



THE OSTEOLOGY AND MYOLOGY 



tract, are both surrounded by well marked muscular fibre. The pairs of Cowper's glands 

 are likewise invested, and very strongly, by separate, dense, bulbous muscles, serving for 

 their compression. 



Muscles of the Anterior Extremity. 



It may be most natural, at any rate I find it most convenient, to consider under this 

 head the muscles by which the anterior extremity is connected with the rest of the body, 



as well as those that lie wholly upon the mem- 

 ber itself. Any division of the body into mus- 

 cular " regions" is purely artificial ; few muscles, 

 comparatively speaking, lying and acting wholly 

 within the limits so mapped out. 



The anterior extremity is attached to the 

 body by the sterno-clavicular articulation and 

 fifteen muscles, distributed as follows : — To the 

 clavicle two, cleido-mastoid and subclavius ; to 

 the scapula seven, trapezius, rhomboideus, serra- 

 tus magnus, levator anguli scapula?, omo-hyoi- 

 deus, atlanto-acromialis,-^ and atlanto-scapularis ; ^ 

 to the humerus five, pectoralis major, in three 

 divisions, latissimus dorsi, and dermo-brachialisj 

 to the ulna one, ej^itrochlearis, a slip from the 

 latissimus dorsi. These will be described in the 

 order in which they are enumerated above. 



Cleido-mastoideus. — Distinct in its whole 

 length from the sterno-mastoid, but with a 

 common origin ; more terete and much smaller. It runs nearly straight downward from the 

 mastoid to be inserted fleshy at the middle of the clavicle. Its course is oblique to that of 

 the sterno-mastoid ; its situation is superficial ; it is in relation, externally, with the anterior 

 border of the slip from the trapezoid. 



Suhclavius. — Of considerable size, and perfectly distinct from contiguous fascial or mus- 

 cular structures ; arises fleshy from the first rib near the sternal extremity, opposite the 

 outer margin of the thoracic prolongation of the rectus alKlominis, and proceeds obliquely 

 outward to be inserted fleshy, into the distal extremity, of the clavicle, tip of acromion, and 

 cleido-acromial ligament. Some of its fibres occasionally blend with those upon the under 

 surface of the cleido-acromial muscle that lies upon the articulation. 



Trapezius. — (Figure 28, c.) This muscle is extremely thin, but of great superficial 

 area, forming a triangular plane that extends from the occiput to the last dorsal vertebra, 



Fig. 28. — Muscles of right shoulder, about three- 

 fourths natural size, (z, acromion; ^, end of clavicle). 



' These names may ho alike unnecessary and unwarr.ant- 

 able; but, as explained further on, I liave no alternative but 

 to impose them, not knowing what, if any, names these two 

 muscles may have already received. The muscle I call " at- 

 lanto-acromialis " may be the same as that described under 

 the name '' trachelo-acroniialis," in, e.g., the horse, where it 

 is said by Owen to arise from the transverse process of the 



atlas and four successive vertebra;, and to spread over the 

 acromial portion of the scapula, and descend as far as the 

 middle of the humerus ; but its disposition, in the opossum, 

 is not strictly correspondent. The other, " atlanto-scapula- 

 ris," may be morphologically the same muscle ; but it is per- 

 fectly distinct in the opossum. 



