wrist and over the surface of the insertion tendon of the ex- 

 tensor poUicis brevis (described below). Behind this, toward 

 the rear margin of the forearm, and arising from the hu- 

 merus by a broad flat head is the extensor carpi radialis lon- 

 gus. This muscle is closely bound to the extensor carpi radialis 

 brevis. The belly of the longus tapers to a tendon after 

 about one-third of the length of the forearm, while the 

 brevis belly extends nearly to the wrist joint. The tendons of 

 these muscles insert on the bases of the second and third 

 metacarpals respectively. 



Behind the extensor carpi radialis muscles are the ex- 

 tensor digitorum communis and the extensor digitorum 

 lateralis. These arise from the lateral condyle of the distal 

 end of the humerus. Their insertion tendons are subdivided 

 into four parts which fan out and attach at the bases of 

 digits II to V in the case of the lateralis and along the 

 phalanges of these digits in the case of the communis. Along 

 the posterior margin of the dorsal musculature is the exten- 

 sor carpi ulnaris. 



Beneath the superficial dorsal muscles are additional ones. 

 The abductor and extensor pollicis brevis arises along and 

 between the distal parts of the radius and ulna. Its fibers 

 taper to a short tendon which overlies the insertion tendons 

 of the extensor carpi radialis muscles and inserts on the 

 proximal end of the first metacarpal. Proximal to this muscle 

 is the supinator which arises from the humerus and inserts 

 on the radius. Behind these muscles is the long, band-like 

 extensor pollicis longus et indicis, which arises from the 

 proximal part of the ulna and inserts by two tendons on the 

 bases of the first and second phalanges. 



The ventral muscle mass has the pronator teres along its 

 anterior proximal margin. This muscle arises from the inner 

 condyle of the humerus and inserts on the radius next to the 

 supinator of the dorsal mass. Behind the pronator is the 

 flexor carpi radialis and behind this a broad muscular band, 

 the palmaris longus. These muscles also arise from the 

 medial condyle. The first inserts on the radiale, the second 

 has a complex insertion through long tendons attaching to 

 the bases of digits II to V. At the wrist a small fleshy belly 

 arises off the palmaris and inserts by tendons on digits IV 

 and V, below the tendons of the palmaris. Cross-muscle 

 fibers on the wrist joint form an adductor pollicis brevis. 

 Behind the palmaris is the flexor carpi ulnaris, which has 

 two heads of origin: one from the olecranon (and in part 

 from the epitrochleo-anconeus — see Figure 14-7) and the 

 other from much of the length of the ulna. The insertion of 

 the flexor carpi lunaris is on the ulnare, and, through the 

 bracing ligament of that bone, on the metacarpals. Associ- 

 ated with this insertion is a small abductor digit! quinti. 



The deeper layer of flexor musculature consists of the 

 several (and varied) bellies of the flexor digitorum pro- 

 fundus. A part of this complex can arbitrarily be identified 

 as the flexor digitorum sublimis. The belly of the sublimis 

 lies near the wrist and its slim tendons pass between those 

 of the palmaris and the profundus proper. 



The muscles of the pelvic appendage The muscles of the 

 thigh are more difficult to identify than those of the fore- 

 limb. Since only a superficial survey of the hind limb mus- 

 cles is intended, the details of origins and insertions will be 

 largely omitted. Viewed laterally (Figure 14-8), the sartorius 

 forms the anterior margin of the thigh. Behind the sartorius 

 is an irregular-shaped tensor fasciae latae, which arises 

 from the anterior end of the ilium and inserts into the 

 fasciae latae covering the outer surface of the thigh. Covered 

 by the fasciae latae and inserting on the head of the femur 

 is the gluteus medius and the gluteus maximus, while 

 distally, covered by the fasciae latae, is the vastus lateralis. 

 Behind the line of the femur is the coccygeofemoralis pars 

 femoralis and then the large biceps femoris, which inserts 

 on the shank through a broad sheet-like tendon or aponeu- 

 rosis. Behind the biceps femoris can be seen a part of the 

 semitendinosus. With the exception of the gluteus muscles, 

 the insertions are broadly over the knee and the lateral as- 

 pect of the proximal part of the shank. Within the aponeu- 

 rosis of the knee is the patella, a sesamoid bone. 



Exposure of the underlying muscles is difficult because of 

 the fasciae latae. By cutting through and reflexing this 

 layer, the gluteal muscles can be exposed. The coccygeo- 

 femoralis and biceps can be severed near their origins and 

 the ends reflexed. Care should be taken to observe the 

 slender band of muscle, the pars tenuissimus of the coc- 

 cygeofemoralis. It arises just below the pars femoralis, ex- 

 tends distally and posteriorly on the inner surface of the 

 biceps femoris, and inserts just inside or along the posterior 

 margin of the biceps femoris. This part is lacking in some 

 specimens. From the origin of the coccygeofemoralis on the 

 transverse processes of two or three caudal vertebrae, a short 

 belly extends down and forward to insert along the margin 

 of the ischium; this can be identified as the pars ischiadicus 

 of the coccygeofemoralis. 



The gluteus medius and maximus have thick and fleshy 

 bellies tapering to broad insertions on the margin of the 

 outer or greater trachanter of the femur. By careful section 

 of these muscles, a deeper layer consisting of the gluteus 

 minimus and pyriformis is exposed. The minimus parallels 

 the ventral margin of the medius and can be seen by lifting 

 that margin. The pyriformis is largely fused with the 

 medius and is difficult to expose. The sciatic nerve trunk 

 passes below (medial to) and behind the pyriformis and 

 separates it from another layer of muscles inserting on the 

 margin of the greater trochanter of the humerus. 



The muscles behind the sciatic nerve are not distinctly 

 separated one from another. The most posterior muscle is 

 the quadratus femoris; its thick belly tapers anteriorly to 

 insert on the posterior margin of the greater trochanter. 

 Above the quadratus is the obturator internus, only the in- 

 insertion portion of which is seen. The obturator internus 

 arises on the inner surface of the pelvis, from the ischium and 

 the margins of the obturator fenestra. The belly tapers and 

 passes over the margin of the ischium; here it forms a thick 



428 



THE MUSCULAR SYSTEM 



