276 ME. F. G. PABSONS ON the [Mar. I 1 '.', 



foar 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-epitroehlearis 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 like 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-epitrcch- 

 learis 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 line, ligamentum nucha), 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 Dipodidas 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 the clavicle. 



Among the Chinchillida?, Chinchilla has an extended cranial 

 origin from the surface of the bulla, while in both it and Lago- 

 stomus some of the fibres pass over the clavicle to blend with the 

 deltoid. 



In the Dasyproctidse 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 (Dasyproeta, Coslogenys). 



In the Caviidse the muscle is divided into two distinct parts and 

 does not reach the clavicle (C. cobaya, Ceredon rupestris, Dolichotis 

 patagoniea l ). 



In the iSciuromorpha the muscle has one continuous origin : in 

 Sciurus and Pteromgs it is not attached to the clavicle, while in 

 Castor it just reaches the outer end of that bone. In Arctomys, 

 SpermopMlus, and 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. 



