The development of the thigh musculature of the chick twelve figures

Abstract The development of the thigh musculature in a series of chick embryos is described and figured. In the earliest the muscular tissue is in the form of two distinct masses lying on opposite surfaces of the limb. Later, both divide into proximal and distal portions at the knee. The proximal portions, by a series of divisions, gradually attain the condition found in the adult thigh. The embryological findings tend to support the theory of the derivation of tetrapod limb musculature from the two opposed (dorsal and ventral) muscle masses of the paired fins of bony fish. The reptilian homologies of the ilio‐trochanterici cannot be definitely ascertained from embryological evidence. The ischio‐femoralis (= ischio‐trochantericus), Previously regarded as dorsal, and the coccygeo‐femorales, previously classed as incertae sedis, are in reality members of the ventral group. The distinction between ‘intrinsic’ and ‘extrinsic’ muscles inserting on the free limb appears to have no embryological or phylogenetic basis in fact. Double innervation (motor) is a primitive condition in tetrapods. Rotation of the avian pubis is correlated with an improved functioning of the obturator in the rotated position coupled with a lack of interference with the other musculature concerned.