6 Practicum I. The Joints and Ligaments. 



the irregular form of the pelvis. Use the scissors to carefully cut away the 

 muscles that have been left attached to the femur and pelvis. 



a. After the flesh about the proximal end of the lemur is mostly re- 

 moved, moving it will show that it has a HEAD imbedded in a socket, and 

 that there is a fibrous CAPSULE extending from the margin of the socket 

 over part of the head. 



b. Push the femur as far as it will go in any direction ; this will ren- 

 der the capsule tense at the opposite side ; cut it here and continue till 

 the head may be extracted slightly from the socket. 



c. Note that its complete removal is prevented by a fibrous cord con- 

 necting it with the bottom of the socket ; this is the ROUND LIGAMENT 

 of the hip joint, present also in man and many animals but absent in the 

 orang which uses its short leg freely as an arm. Cut the ligament. 



6. Compare the two ends of the femur. The subspherical head, 

 on the constricted neck, enters into the composition of a "ball-and-socket 

 joint ;" the distal end forms at the knee a "hinge-joint." The patella 

 (knee-pan) has been removed. The movements at either end are similar 

 to those in man. 



7. The Periosteum. Near the distal end of the bone note the cov- 

 ering of fibrous membrane, the PERIOSTEUM. Divide it at any point, pref- 

 erably with a pocket-knife or arthrotome. Insert the tracer between it 

 and the bone ; strip it from the bone for a considerable area. Near the 

 ends of the bone there may be seen vessels passing from it into the bone ; 

 in the dried bone the small orifices for these vessels may be detected. 



8. The Marrow. Transect the femur with saw, nippers or hatchet. 

 The shaft of the bone forms a tube whose cavity is filled with a kind of 

 fat, the MARROW. The ends are solid but of a spongy texture. 



9. Remove the right leg at the hip. Trim oflf remnants of flesh 

 with the scissors and preserve for use at Pr. II. 



10. The Skin Muscles. On PI. II, the irregular lines crossing be- 

 tween the words THORAX and ABDOMEN indicate the cut edge of a thin 

 muscle the caudal part of which is supposed to have been removed with 

 the skin ; the cephalic part narrows to be attached to certain muscles of 

 the arm. 



a. In the cat, as in most quadrupeds, in addition to the ordinary 

 muscles of the limbs and those of the trunk which are attached to bones, 

 there is a nearly continuous sheet of muscle in close relation with the 

 skin ; this enables the horse, for instance, to shake off a fly, while the 

 attachment to the arm increases the efficiency of that limb in ordinary 

 locomotion or climbing. In man the skin muscles are present only on 

 the neck and head, mainly as organs of expression. 



ii. At about the middle of the left side of the thorax, as indicated 

 on Fig. i, make two incisions crossing one another at right angles and 

 about 5 cm. (2 in.) long. Together they constitute a crucial incision, 



a. These first incisions should divide only the skin, an apparently 

 single, tough layer. 



12. There are thus established four triangular flaps of skin. With 

 the forceps grasp the corner of one of these flaps, lift it and with the 

 scalpel dissect it from the subjacent parts. Even if the incisions have 

 divided more than the skin the latter may be isolated by taking care to 

 lift only a single layer of tissue, the ental surface of which is white or 

 dark, but not red or pink. 



