o/^Cyclothurus didactylus. 247 



Since this muscle coexists with an upward prolongation of 

 the rectus ahdominis, it can scarcely be regarded as a " late- 

 ralized" slip of the rectus, as suggested by Prof. Macalister*. 

 It is, moreover, completely separated from the rectus by a 

 muscular stratum composed of the thoracic fibres of origin of 

 the obliquus externus. Cuvier figures the muscle very clearly 

 (pi. 257. fig. 2), but terms it " scalane, portion exterieure ou 

 inf^rieure." In his plate of the myology of Myrmecophaga 

 tamandua (pi. 262), it is represented as passing over the serra- 

 tus magnus. I am inclined to regard this muscle, as evidently 

 did Cuvier, as a downward detachment from the scalenus. 



Mr. Wood describes a similar muscle as occurring in man, 

 under the name of " supracostal " (Proc. Roy. Soc. June 1865, 

 p. 3, and May 1867, p. 523). A like muscle, too, is recorded 

 and figured as a human abnormality in Virchow's ^ Archiv/ 

 Nov. 1867 (Taf. 6. fig. 1). 



The rhomboidei are fused together into one muscle. They 

 arise from the upper third of the dorsal vertebral region, and 

 are inserted along the whole of the superior (or posterior) costa 

 of the scapula ; covered by the trapezius. I did not find any 

 occipito-scapular slip. 



The trapezius arose from the occiput, from the spines of the 

 cervical vertebra3, and from the vertebral spines in the upper 

 third of the dorsal region. It was inserted along the posterior 

 (superior) edge of the spine of the scapula, and into the distal 

 fourth of the clavicle. Meckel notices (Archiv, p. 38) the 

 clavicular insertion. 



The acromio-basilar was not present. 



The serratus magnus was well developed. It seemed to be 

 made up of three factors : — 



1. The highest, evidently corresponding to the levator sca- 

 pulae, arose from the two or three lower cervical vertebrae, and 

 was inserted into the superior angle of the scapula and, for 

 some little distance, along the superior costa of the bone, being 

 overlapped by the highest fibres of origin of the rhomboideus. 



2. The smallest factor, inserted into the inner face of the 

 scapula, internal to the division just described, arose from the 

 first rib, just external to the insertion of the scalenus anticus, 

 with the outermost fibres of which muscle it appears to be in 

 intimate connexion. 



3. The lowest, corresponding to the serratus magnus of 

 anthropotomy, arose from the second to the seventh ribs, in- 

 clusive, external to the rectus abdominis, being overlapped at 

 its origin by the outer border of this muscle. A few fibres, too, 



* " On the Myology of Sradypm tridadylus,''' Ann. & Mag. Nat. Hist. 

 July 1869, p. 55. 



