134 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



applicable to either animal, differences between them being specifically noted 

 wherever necessary. 



i. The dermal or integumental muscles.— Skin the animal and in doing so 

 note the structures named in the following paragraph. (If the animal has 

 already been skinned, this part of the work will have to be omitted.) In skin- 

 ning, make a median dorsal incision from the base of the tail to the back of the 

 head. Be sure that this and following incisions cut through the skin only. 

 Make an incision through the skin around the throat, around ankles and 

 wrists, and incisions along the outer surface of the limbs. Connect these with 

 the median incision. Loosen the skin along the incisions and gradually work 

 the skin loose from the muscles, using fingers and back of the scalpel. Avoid 

 as far as possible the method of cutting the skin from the body, as one is liable 

 to cut into the muscles by this procedure. Work from the dorsal side toward the 

 ventral side. Leave the skin on the head and on the perineal region for the present. 



The following points should be noted during the skinning. The skin is 

 connected with the underlying muscles by a loose weblike material, the subcuta- 

 neous connective tissue or superficial fascia, often impregnated with fat. Below 

 this is the much firmer and tougher connective tissue on the surface of the muscles, 

 forming the deep fascia. Passing from among the muscles into the skin will be 

 seen at regular intervals, which represent the segments of the body, a slender 

 cord, composed of an artery, a vein, and a sensory nerve. These may be severed. 

 Other blood vessels, not segmentally arranged, will also be seen passing onto the 

 under surface of the skin, from anterior and posterior regions toward the middle. 

 The arteries are colored by an injection mass and are readily recognized. The 

 veins are usually of a very dark reddish-brown color. All vessels to the skin 

 should be severed. 



When the skin has been loosened to the sides'of the animal, there will be noted 

 a thin layer of muscle fibers on its under surface, appearing like a fine striping. 

 Toward the chest and shoulder region this assumes the form of a thin sheet. 

 This muscle is a dermal or skin muscle, the panniculus carnosus or cutaneous 

 maximus. It covers the entire lateral surface of the thorax and abdomen, being 

 more prominent anteriorly. On continuing to skin forward and ventrally 

 the muscle will be found to take its origin from the outer surface of a muscle 

 (latissimus dorsi) situated posterior to the shoulder, and from the axilla in the 

 cat, the medial side of the humerus (rabbit), and from the linea alba and various 

 points on the ventral side of the thorax in both animals. These points of origin 

 should be cut through and the cutaneous maximus removed with the skin to 

 which it generally adheres. The muscle is inserted on the skin and serves to 

 shake the skin. In man this muscle is degenerate. It is an outgrowth of the 

 latissimus dorsi muscle. 



There is one other dermal muscle, the platysma. This will be found on the 

 under surface of the skin of the neck and head, and consists of many different 



