Practicum III. The Thoracic Parietes. 



19 



8 14. Cutting the Ribs. The removal of the remaining portion of the parietes involves 

 division of the ribs. For this the rented practicum scissors must not be employed. A 

 strong pair is required and unless the student has them among his own instruments the 

 instructor should be called upon. With old cats even nippers may be needed. 



$ 15. Cut dorsad from the angle between the eleventh and twelfth 

 cartilages (see Fig. i) until the thick spinal muscles are reached, just 

 caudad of the thirteenth rib. Then cut cephalad to the first rib and 

 remove the other ribs and the intercostals. 



TRACHEA 

 ESOPHAGUS 



FIG. 6. RIGHT SIDE OF THE CAT'S THORAX. 



Diagram indicating the mode of dividing the right thoracic wall, while the cat is on 

 its back, its head to the left. The letters of the word sternum are placed on the seven 

 segments of the MESOSTERNUM, the PRESTERNUM and XIPHISTERNUM being left blank ; 

 see PL i. The ribs are numbered i 13, the numbers being placed just dorsad (under in 

 the figure) of the lines of junction with their respective cartilages. The lines of incision 

 are indicated by the interrupted lines, beginning at the 6th cartilage. 



16. Caution. In the following examination avoid displacing the viscera more than 

 directed and particularly all pulling or lifting of the sternum, on account of a delicate 

 attachment to be described in # 29. Any liquid in the thorax may be sopped with absorb- 

 ent cotton. 



17. The Thoracic Parietes. Before displacing the contentsof the 

 cavity thus opened to view, note the constitution of the walls or PAR- 

 IETES. Dorsad are the ribs and intervening intercostals ; ventrad, the 

 cartilages and intercostals ; the ribs are supported from the spine, and the 

 cartilages directly or indirectly join the sternum. Cephalad, the slight 

 interval circumscribed by the spine, the sternum and the first pair of ribs 

 and their cartilages, is wholly occupied by the trachea and esophagus, 

 blood-vessels, nerves and connective tissue ; these will be seen later. The 

 broad base of the thorax is formed by the DIAPHRAGM ; this will be more 

 fully studied at Practicum IV ; at present there is to be seen only a nar- 

 row area of it under the overhanging strip of the lateral parietes. 



18. The Pleura. Look at the ental surface of the removed lateral 

 parietes and note that it is smooth and shining ; the cut edge may be sep- 

 arated as a delicate serosa, the PLEURA. If the overhanging strip of 

 parietes left at the caudal margin of the opened thorax is reverted it will 

 be seen that the pleura covering its ental surface is continued upon the 

 diaphragm. Observe further that the visible surfaces of the exposed 



