OCR Text |
Show 1894.] MYOLOGY OP RODENTS. 259 In Hystrix and Sphingurus only one muscle can be made out; it rises from all the cervical transverse processes and is inserted into the anterior four ribs. In Lagostomus, Agouti, and Ccelogenys the muscle rises from all the cervical transverse processes ; the fibres from the anterior three or four are attached to the outer surfaces of the ribs from the second to the fifth and interdigitate with the serratus magnus ; in Lagostomus the sixth rib is reached. The fibres from the posterior transverse processes are attached to the first rib behind the subclavian artery. In the Caviidae the fibres which are attached to the side of the chest come from the 3rd and 4th cervical transverse processes, and are inserted into the 3rd and 4th ribs. The slip to the first rib comes from all the cervical transverse processes. Muscles of the Anterior Extremity. The Pectoral Muscles.-As the pectoralis major and minor are not always distinct muscles, I have followed Owen's example in his description of Capromys L, and have divided the whole pectoral mass into four different parts, which are usually easy to make out. These four parts have generally the following attachments:- (a) The most superficial part, rising from the anterior portion of the sternum and sometimes the sternal end of the clavicle, is inserted fairly low down on the humerus, often crossing obliquely the fibres of the next part, which is on a deeper plane. (B) This portion rises from tbe greater part of the sternum posterior to the last and is inserted into the pectoral ridge of the humerus. (y) The abdominal portion rises from the linea alba; being closely connected to and embraced by the panniculus carnosus, its fibres pass deep to 3, and are usually inserted into the top of the pectoral ridge and the upper extremity of the humerus. (3) The deep portion, which perhaps corresponds to the pectoralis minor of human anatomy, rises from the cartilages of some of the true ribs, close to their junction with the sternum. The fibres run upwards and outwards to the outer part of the clavicle, coracoid, or shoulder-capsule. In the Octodontidae a and B are almost if not completely fused. y goes to the lesser tuberosity of the humerus. 2 rises from the cartilages of 3rd to 6th ribs aud is inserted into tbe outer part of the clavicle and coracoid process. This arrangement applies to Myopotamus, Aulacodus, and Capromys pilorides; it also agrees with Dobson's description of the muscle in Capromys melanurus2. 1 P. Z. S. 1832, p. 74. 2 P. Z. S. 1884, p. 234. |