BY DENE 6. FRY. 779 



and nearly straight. Starting from the posterior margin of the 

 sternal plate some little distance from the linea alba, it runs out- 

 wards and backwards at an angle of about 45', crossing the first 

 and anterior two-thirds of the second segment of the rectus. The 

 portio externus (pae.) of the muscle is long and strap-like, and 

 lies just external to, and touching the edge of the portio internus 

 along its whole length. It extends along the length of the 

 abdomen, is of equal width throughout, and enters its inseition 

 beneath the deltoid together with the inner portion. It appears 

 to V)e bound in the same fascia as the portio internus, from 

 which, however, it is easily separated. 



In K. pulchra, the portio interitus (Plate Iv., fig. 1, j^ai.) is also 

 fan-shaped, but with this, the similarity between the pectorales 

 of the two forms ends Two peculiarities of the inner portion 

 are of a most unusual nature. Firstly, the most anterior fibres, 

 i.e., those nearest tlie pars sternalis, overlap that muscle, and to 

 a great extent hide it from view, finding attachment on the 

 median line of the sternal plate, inside the origin of the fibres of 

 the pars sternalis, -which do not meet those of the muscle of the 

 opposite side. Secondly, the portion of the pectoralis abdominis, 

 which attaches to the sternum, is in contact with its fellow along 

 the middle line of the breast-plate. This peculiar arrangement 

 is made clear by the figure in Plate Iv., in which the greater 

 part of the right pectoralis is shown dissected away. The abdo- 

 minal line of origin of the pectoralis abdominis is curved, and 

 terminates postero-laterally on the first inscriptio tendinea. The 

 portio externus {^\site Iv., fig.l, pae.), although quite distinct from 

 the inner portion, is connected to it and to the integument by 

 multitudinous fibres, which seem to arise from the fascia invest- 

 ing the muscle. It is triangular in shape, thus differing from 

 the condition in L. dorsalis, and is somewhat longer than the 

 inner portion. The inner edge of the portio externus overlaps 

 the outer edge of the inner portion to a considerable extent, as 

 the pins in the figure indicate (Plate Iv., fig.l). When seen 

 from the ventral aspect, the triangular nature of the outer por- 

 tion is not evident, as only the innermost edge is visible, the 

 greater portion of the muscle lying on the side of the body. 



