Contributions to Bird-Anatomy and Classification. 11 



of the postacetabular ridge/' as the ridge separating the 

 lateral from the dorsal surface of the postacetabular area of 

 the pelvis raay be called^ " as well as from the posterior border 

 of the ischium^ as far forward as its junction with the pubis/' 

 Its fibres converge and become blended with those of the 

 extensor femoris, forming with them a broad thin aponeurosis 

 which covers the front of the knee and is inserted into the 

 tibia-head — the patella, when present, being developed in it. 

 The degree of development of this muscle (whose cut surfaces 

 are marked ^/ in fig. 5) varies much in different groups of 

 birdsj and in some may be entirely absent, e. g. the Bucero- 

 tidse and Palamedeidse. As a rule, it is not small. In the 

 paper on Chauna* a table will be found stating the degree 

 of development of this muscle in the greater number of fami- 

 lies (/. c. p. 199). 



(3) The semitendinosus. — Generally a broad flat ribbon- 

 shaped muscle, bordering the contour (sometimes together 

 with another muscle, the semimembranosus) of the fleshy part 

 of the thigh behind. It arises from the transverse process of 

 the first free coccygeal vertebra, and from the fibrous mem- 

 brane between this and the ilium -, it is inserted into the inner 

 side of the head of the tibia (at least when the muscle next to 

 be described is absent) . 



(4) In many birds a " a rhomboidal sheet of muscle, arising 

 from the anterior end of the linea aspera " (a muscular line 

 on the under surface of the femur) joins the last-named 

 muscle " anteriorly by an oblique tendinous raphe, which 

 continues down the back of the leg superficially.'" When 

 present, most of the main semitendinosus joins this accessory 

 head to be continued down the leg. 



(5) The femoro -caudal. — This is a thin, narrow, elongated 

 muscle, which is covered above by the gluteus primus (if pre- 

 sent) and the biceps cruris, below by the semitendinosus. 

 Arising from the last two coccygeal vertebrae, it is inserted 

 into the linea aspera of the femur at about one third its 

 length (in the Fowl) from the trochanter. 



(6) In many birds the femora-caudal is joined by an acces- 



* " On tlie Anatomy of Cliauna derbiana" &c., P. Z. S. 1876, pp. 189- 

 200. 



