TRUNK. 115 



form a pair of hollow cones, which fit accurately into the 

 cavity of the two similar cones of the myotome in front and 

 are themselves filled by those of the myotome behind. 

 Between and superficial to the bases of the cones there is a 

 wedge of soft muscle of a dark reddish-brown colour. 

 0. 0. D a. 



C. 115. Transverse section through the body of a Mackerel 

 (Scomber scomber), showing the concentric rings due to 

 the section of muscle-cones of successive myotomes and the 

 division of the trunk-muscles into dorsal and ventral 

 columns by a longitudinal lateral septum. The brown 

 superficial lateral muscle in this specimen has assumed a 

 lighter tone than the general trunk-muscles. The pattern 

 formed by the cut edges of the intermuscular septa is here 

 far simpler than in the Dog-fish, and indicates a less com- 

 plicated form o myotome. 0. C. 63 D b. 



C. 116. A portion of the trunk of a Python (Python sebce), 

 dissected from the left side to show the musculature external 

 to the ribs. A lateral cutaneous muscle (cutaneus externus), 

 composed of numerous ribbon-like strands, arises high up on 

 each rib and passes downwards and backwards to the skin. 

 It is opposed by the cutaneus internus, arising in separate 

 fasciculi from the point of each rib and passing forwards to 

 the ventral parts of the skin. On either side of the back 

 there is a large composite mass of muscle, which forms a 

 specially strong and important feature in the muscular 

 system of the constricting serpents. Its chief components 

 are the capito-vertebralis and the retractor costas biceps. 

 Beneath the strands of the cutaneus externus lies a sheet 

 of muscle composed of intercostales superiores and inferiores, 

 posteriorly they have been separated to show their attach- 

 ments. Each fasciculus of these muscles passes over from 

 12-16 ribs between its origin and insertion. In the lower 

 part of the specimen the intercostales proprii are visible, 

 passing from rib to rib. 0. C. 63 I. 

 D' Alton, Arch. f. Anat. 1834, p. 432. 



12 



