PRACTICUM II. DISSECTION OF THE CAT'S ARM. 



PLATES REQUIRED : I, II, III, IV, V. 



A ligamentous skeleton of the arm should be available for examina- 

 tion if possible. If all are supplied contiguous students should have a 

 right and a left. A leg was saved from Pr. I. 



i. Review the Segments, Joints and Larger Bones of the Arm from 

 Plates I and II ; the scapula now appears to constitute a segment of the 

 limb instead of a part of the trunk. 



2. Learn the Technical Names of the Five Digits (fingers] ; POI,- 

 LEX (thumb); INDEX (forefinger); MEDIUS (middle-finger); ANNULARIS 

 (ring-finger) : MINIMUS (little-finger). On PL V all are visible and named 

 excepting the minimus. The pollex is the shortest, its attachment is 

 most proximal and in the cat it is notopposable to the other digits like the 

 human thumb. 



3. Determine whether the Arm be Right or Left as follows : Hold 

 it in front of you, the hand downward and the elbow toward you ; if the 

 pollex is toward your right the arm is the left ; if toward your left the 

 arm is the right. 



4. Determine the Aspects of the Arm. That which bears the pol- 

 lex is next the thorax, and is the "inner" or ulnar ; the other is the 

 "outer" or radial. 



a. There is liability to some confusion here since the pollex is in 

 line with the radius ; but in the cat the radius is crossed upon the ulna so 

 as to rotate (pronate) the hand and bring the pollex upon the ulnar side. 



b. The student may illustrate the two conditions upon his own arm 

 as follows : If the hand be placed upon the table with the palm upward 

 the pollex is "outer" and the two bones of the antibrachium (ulna and 

 radius) are parallel, the radius as a whole lying upon the ''outer" side. 

 But if the palm be turned down the distal end of the radius crosses to the 

 "inner" side of the ulna and the pollex likewise comes to be on the ulnar 

 or "inner" side of the limb, as in the cat. 



5. Remove the Skin from the Arm. In Pract. I, 4, h, the skin 

 was cut around the arm between the elbow and shoulder. It may be 

 "stripped" to the wrist, everted as a closely-fitting glove-finger may be 

 turned inside out. Cut it at or distad of the wrist. Its complete removal 

 may require slitting along the dorsum of each digit. 



6. With the Scissors Trim off the Muscles remaining attached to the 

 dorsal or vertebral border of the scapula. Since the dorsal border of the 

 scapula is convex the concavity of the curved scissors should be applied 

 to it. The ragged remnants of the skin-muscle attached to the latissmus 

 should also be cut off. 



^ 7. With young cats the border of the scapula consists of a strip 

 of cartilage which later is converted into bone. With the arthrotome or 

 a pocket-knife cut a notch through the cartilage into the bone ; the former 

 may be broken from the latter along their line of junction. 



