PHYSIOLOGY PRACTICUMS. 



PART II. THE THORAX AND ABDOMEN. 



PRACTICUM III. THE THORAX OF THE CAT. 



PLATES REQUIRED : I, II, IV, VI, VII. 



\ i. Transecting the Neck. For this and the next practicum it will be convenient to 

 separate the head from the trunk at about the point indicated in Fig. 2, corresponding 

 nearly with the middle of the word NECK on PI. II ; this will leave most of the neck 

 with the head. Draw the head nearly into line with the trunk ; with a sharp arthrotome, 

 by a steady circular incision, divide the soft parts as completely as possible to the bone ; 

 let the cat be held with its back on a board : place in the incision the edge of a sharp 

 hatchet or cleaver and strike it forcibly enough to cut the spine at one stroke. 



2. Examine the skeleton of man and the cat. Bear in mind that 

 the components of any longitudinal series, as vertebrae, ribs or cartilages, 

 are always numbered beginning with the most cephalic. 



3. Place the cat on its back, the neck to the left. As compared 

 with PI. i, the ventral and dorsal regions are inverted. 



4. Removal of the Extrinsic muscles. In doing this take pains not 

 to cut so deeply as to open the cavity of the thorax. 



a. Grasp the cut end of either PECTORAL MASS (PI. IV. A G) pull 

 toward the meson, and trim off along the sternum. 



b. The RECTUS is a ribbon-like muscle lying upon the cartilages just 

 laterad of the sternum (PL IV). At about the middle of its length push 

 the scalpel handle under it ; raise it a little ; transect it and dissect off 

 the halves respectively cephalad and caudad. 



c. Laterad of the cephalic part of the rectus are attached several 

 muscles of the neck ; cut close to their attachments upon the ribs. 



d. Farther dorsad are the remnants of the muscles referred to in 

 Pr. I ( 20) as suspending the thorax between the scapulas ; note that its 

 thoracic attachments constitute more or less distinct digitations, like the 

 teeth of a saw, whence the name SERRATUS. In removing it cut with 

 the scissors along the length of the ribs and cartilages, that is in a general 

 dorso-ventral direction, rather than lengthwise of the thorax as a whole. 



e. On the caudal portion of the thorax remove all muscles for i 2 

 cm. beyond the last ribs, but do it very cautiously so as not to open the ab- 

 domen. 



? 5 The Spinal Muscles. Under this general title may be conveniently designated 

 the thick mass lying along the dorsal part of the thorax (Fig. i). Parts of them illustrate 

 the way in which a slender tendon may be formed by the convergence of a thin FASCIA 

 from the surface of a muscle. These muscles need not be removed. 



6. On the cut end of the neck note the two tubes, TRACHEA and 

 ESOPHAGUS, the former ventrad and open, the latter dorsad and collapsed. 

 Expose them as far as the first ribs by carefully cutting away the muscles 

 and connective tissue, but do not pull the soft parts cephalad lest the thorax 



