THE MUSCLES OF THE LIMBS. 49 



the himl-linro. On the other hand, a musolc, the obturator 

 iiitenius, attached to tlie inner surface of the ischiopubio fon- 

 tanelle, and winding round to the femur, has no homologue in 

 the upper extremity of the higher Yertehrata, unless it be the 

 so-called cora-:obrachialis, which arises from the inner surface 

 of the coracoid in many Sauropsida. 



Muscles of the Antehraohiuin and Crus. — On the dorsal 

 aspest of the fore-limb, as of the hind-limb, certain muscles 

 (trise in part from the arch, and, in part, from the bone of the 

 proximal segmeni of the limb, and go to be inserted into the 

 two bones of the second segment. These are, in the fore- 

 limb, the triceps extensor and the supinator brevis / in the 

 hind-limb, the quadriceps extensor. 



There is this difference between these two homologous 

 groups of muscles — ^that in the fore-limb, the principal mass 

 of the muscular fibres goes, as the triceps, to be inserted into 

 the post-axial bone (ulna), and the less portion, as supinator 

 brevis, into the pre-axial bone (radius) ; whereas, in the hind- 

 limb, it is the other waj', almost the whole of the muscular 

 fibres passing, as the quadriceps, to the pre-axial bone (tibia), 

 the tendon commonly developing a sesamoid patella/ while 

 only a few fibres of that division of the quadriceps which is 

 called the " vastus externus " pass to the post-axial bone 

 (fibula). 



On the ventral aspect, the fore-limb presents three mus- 

 cles, arising either from the pectoral arch, or from the hume- 

 rus, and inserted into the two bones of the forearm. On the 

 pre-axial side are two muscles ; one double-headed, the biceps, 

 arising from the scapula and the coracoid, and inserted into 

 the radius. A second, the supinator longus, passes from the 

 humerus to the radius. On the post-axial side, the brachialis 

 anticus arises from the humerus, and is inserted into the ulna. 

 The hind-limb has two muscles, the sartorius, arising from the 

 ilium, and the gracilis, from the pubis, in place of the biceps 

 braohii, and inserted into the pre-axial bone, the tibia, which 

 corresponds with the radius. Two other muscles, the semi- 

 membranosus and semi-tendinosus, pass from the ischium to 

 tlie tibia, and replace, without exactly representing, the su- 

 pi?iator longus. Corresponding with the brachialis anticus 

 is the short head of the biceps femoris, arising from the femur, 

 and inserted into the post-axial bone of the leg, the fibula. 

 The long head of the biceps femoris, which proceeds from the 

 ischium, appears to have no representative in the fore-limb. 



In the fore-limb, a muscle, the pronator teres, passes ob- 

 3 



