Myology of the pectoral girdle of the golden hamster
Spooner, William Merton
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In the literature which is written on rodent myology there is not much reference made to the morphology of the golden hamster. Parsons (1896) reports on some hamsters that he dissected. Priddy and Brodie (1948) have published the only recent work on the morphology of the golden hamster. This study is concerned with the myology of the pectoral girdle of the golden hamster. The pectoral girdle is compared with that of the laboratory rat (Greene, 1935), the wood rat (Howell, 1926), the kangeroo rat (Howell, 1932), the pocket gopher (Hollinger, 1916) and the rabbit (Bensley, 1938). Parsons work on the comparative myology of the sciuromorphine, hystricomorphine and myomorphine rodents (1894 and 1896) is referred to extensively. The following muscles are included in this study: M. clavotrapezius, M. acromiotrapezius, M. spinotrapezius, M. sternomastoideus, M. cleidomastoideus, M. subclavius, M. atlantoscapularis, M. occipitoscapularis, M. levator scapulae, M. seratus magnus, M. rhomboideus anticus, M. rhomboideus posticus, M. acromiodeltoideus, M. spinodeltideus, M. suspraspinatus, M. infraspinatus, M. subscapularis, M. teres major, M. teres minor, M. coracobrachialis, M. pectoralis, M. latissimus dorsi, M. epitrochlearis, M. anconeus, M. triceps longus, M. triceps lateralis, M. triceps medialis, M. biceps brachii and M. brachialis. The origins and insertions or the following muscles had the normal relationships in the golden hamster: sternomastoideus, cleidomastoideus, subclavius, acromiodeltoideus, spinodeltoideus, supraspinatus, infraspinatus, subscapularis, teres major, latissimus dorsi, anconeus, triceps longus, triceps lateralis, triceps medialis and brachialis. The trapezius muscle in the hamster is clearly divided into three parts: clavotrapezius, acromiotrapezius and spinotrapezius. The origin of the spinotrapezius showed some variation in the animals that were dissected. The trapezius complex of muscles showed differences in the laboratory rat (Greene, 1935) and in the pocket gopher (Hollinger, 1916). The atlantoscapularis in the hamster arises from the atlas only, but in the rabbit the atlantoscapularis arises from the sphenoocipital synchondrosis. Parsons reports that in the sciuromorphine and hystricomorphine rodents (1894) the origin may be from either place mentioned above. The occipitoscapularis is a distinct muscle in the hamster, laboratory rat and the wood rat. Bensley (1938) treats this muscle as a part of the levator scapulae complex. Parsons (1894 and 1896) and Howell (1932) treat the occipitoscapularis as part of the rhomboideus complex. The levator scapulae in the hamster originates from the lateral processes of the last three cervical vertebrae and from the first three ribs. The other animals in this study vary considerably as to points of origin. The serratus magnus in the hamster originates from the third to the ninth rib. The other animals in this study vary considerably as to points of origin. Most of the authors in this study treated the levator scapulae as part of the serratus magnus complex and treat them both as one muscle. Greene (1935) treats them as separate muscles and so does Howell (1926). The rhomboideus complex in the hamster can be divided into a rhomboideus anticus and a rhomboideus posticus. Most of the authors consider them as one muscle consisting of two parts. Parsons (1896) considers the occipitoscapularis as a component of the rhomboideus complex and terms it the rhomboideus capitis. The teres minor is not distinguishable as a separate muscle in the golden hamster and is treated as part of the infraspinatus complex. Parsons (1896) reports that this is true in all the Myomorpha. The other authors treat the teres minor as a distinct muscle. In the hamster the coracobrachialis is treated as one muscle. Howell (1932) describes a pars profunda and a pars media in the kangeroo rat. Parsons (1894 and 1896) divides the coracobrachialis into three parts. The other authors included in this study treat the coracobrachialis as just one muscle. The pectoralis muscle in the golden hamster is divided into four parts. The first and second elements insert upon the deltoid crest of the humerus while the third and fourth elements are inserted slightly higher on the shaft, head and tuberosities of the humerus. The laboratory rat (Greene, 1935) has a xiphihumeralis that inserts upon the coracoid process of the scapula. The wood rat (Howell, 1926) is very similar to the hamster in the morphology of the pectoralis muscle. Parsons (1894 and 1896) describes a fourth part arising from some of the true ribs and inserting onto the shoulder capsule. Bensley (1938) reports that in the rabbit there is a pectoral element running from the sternum to the spine of the scapula. In the hamster and the wood rat the epitrochlearis runs between the latissimus dorsi and the inner elbow. In both animals it is a ribbon-like muscle and has a muscular origin and insertion. In the laboratory rat (Greene, 1935) the epitrochlearis is more compressed and has a tendinous origin and ins ertion. Bensley (1938) and Parsons (1894 and 1896) do not report this muscle. The biceps brachii in the golden hamster has two heads as is characteristic of the Myoraorpha (Parsons, 1896). The insertion of the biceps brachii varies slightly in the different animals of this study. In the pocket gopher (Hollinger, 1916) it inserts on the ulna. The insertion of the biceps brachii in the laboratory rat (Greene, 1935) is similar to that in the hamster, which is on the radius. The wood rat (Howell, 1926) is identical with the hamster. In the kangeroo rat (Howell, 1932) the two heads remain separate and the long head inserts upon the ulna while the short head inserts on the radius.
Thesis (M.A.)--Boston University