The appendicular muscles of Necturus macnlpsus. 407 



girdle, and is confined in Necturus to the posterior half of the pubo- 

 ischiadic plate, although in most urodeles it extends over the 

 entire ventral surface, completely concealing the puboischiofemoralis 

 externus, which is here exposed anteriorly. The muscle is in the 

 form of a triangulär sheet, and takes its origin from the median 

 line of the pubo-ischiadic plate for a little more than the posterior 

 third of its extent, the surface of origin being slightly augmented 

 through the development of a low median ridge, the crista mus- 

 cularis. From this origin the fibers converge to the knee and 

 lower leg. in which region they become inserted. 



The muscular sheet thus defined is marked by two peculiar 

 features, a raphe and a tendon. The raphe begins at the posterior 

 border, about midway between origin and insertion, and runs ante- 

 riorly, at right angles to the fibers, fully half-way through the muscle, 

 presenting the appearance of a broad and rather deep scar. It 

 serves as the point of insertion for M. caudali-puboischiotibialis, a 

 band-like muscle which comes up from the tail in Company with 

 two other caudal muscles, and is inserted into the raphe at the 

 posterior border of the puboischiotibialis, the fibers of the two muscles 

 involved running alniost at right angles to each other. Aside from 

 this caudal muscle there is an accessory bündle of fibers, situated 

 upon the deeper (dorsal) surface of the puboischiotibialis, blended 

 with the main muscle at the origin and inserted into the deep sur- 

 face of the raphe. This bündle evidently represents the ischioflexorius 

 of other urodeles, although it is here not sufficiently distinct to be 

 considered a separate muscle. 



The second feature mentioned above, the tendon, marks the 

 antero-lateral border of the muscle, and is complicated as well as 

 variable in its relationships. When best developed it is quite broad, 

 visible superficialis, and serves to define the boundary between this 

 muscle and M. pubotibialis. It usually forms the direct continuation 

 of the fibers of about the anterior third of the muscle, that is, of 

 those not affected by the raphe, but in addition to these it receives 

 a variable number of fibers along both edges; those inserting on the 

 postero-medial edge arise from the distal side of the raphe, and those 

 on the antero-lateral edge are derived from the adjacent muscle, 

 M. pubotibialis. These relations are subject to considerable individual 

 Variation, and the tendon itself may vary in size from that described 

 above to a delicate thread, sunk between the fibers and not visible 

 superficially. In some cases it may seem more like a thin septum, 



