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Show 276 MR. P. G. PARSONS ON T H E [Mar. 20, four ribs, and the lumbar aponeurosis. It is inserted by a flat tendon into the upper part of the anterior surface of the humerus internal to the pectoral ridge. Its relation to the teres major has already been noticed under the head of that muscle. Very often some of the fibres of the muscle are continued across the axilla to blend with the pectoralis major. The dorso-epitrochlearis is always present, occasionally blending with the fascia over the triceps, but more often being well marked and inserted into the olecranon process. In the Hystricidae and in Castor the tendon of the muscle is inserted in front, behind, and below the teres major in such a manner that a section of it would appear hke the letter J. In Capromys and Castor a number of fibres were seen passing in front of the axillary vessels to the pectoral. The dorso-epitrochlearis is, perhaps, least well seen in Lagostomus and Dasyprocta, best in Sphingurus. Trapezius.-The trapezius may or may not be divided into an anterior and posterior portion, separated by a fascial interval. Its origin is from the occipital curved hue, ligamentum nuchae, and the thoracic spines, except the last three or four. It is inserted into the spine and acromial process of the scapula, and often into the clavicle. In the Dipodidae the muscle is divided into two distinct parts, the anterior of which is the larger, and goes to the acromion and the greater part of the spine : the posterior is only attached to the root of the spine (D. cegyptius, D. hirtipes, Alectaga indica). In the Octodontidae the two parts of the muscle may be made out, but they are practically continuous : the insertion is continued on to the outer part of the clavicle ( Octodon, Aulacodus, Capromys). In Hystrix the muscle is single and does not reach tbe clavicle. Among the Chinchillidae, Chinchilla has an extended cranial origin from the surface of the bulla, while in both it and Lagostomus some of the fibres pass over the clavicle to blend with the deltoid. In the Dasyproctidae the muscle is divided into two parts, some of the cranial fibres being prolonged down on the outer side of the humerus for some distance (Dasyprocta, Ccelogenys). In the Caviidae the muscle is divided into two distinct parts and does not reach the clavicle (C. cobaya, Ceredon rupestris, Dolichotis patagoyiica *). In the Sciuromorpha the muscle has one continuous origin : in Sciurus and Pteromys it is not attached to the clavicle, while in Castor it just reaches the outer end of that bone. In Arctomys, Spermophilus, aud Xerus the inner part of the muscle is separated from the rest by the levator claviculae, and lies over the cleido-mastoid, making that muscle appear double : in Arctomys this slip is shifted so far inwards that it becomes attached to the front of the sternum. Rhomboideus.-The rhomboideus capitis major and minor rise by one continuous origin from the superior curved line of the 1 Beddard, P. Z. S. 1891, p. 236. |
