30 DISSECTION OF THE CAT 



5. The Diaphragm is the musculo-tendinous par- 

 tition separating the abdominal and thoracic cav- 

 ities. The muscular portion of the diaphragm at 

 its circumference arises ventrally from the ensi- 

 form cartilage, laterally from the last five ribs and 

 the aponeuroses of the muscles of the back, and 

 dorsally from the bodies of the lumbar vertebrae 

 by two thick slips or crura. From all these 

 points the fibres converge, to end in the central 

 tendon. The diaphragm is pierced by the oesoph- 

 agus, aorta, and inferior vena cava. 



MUSCLES OF THE THORAX. 



i. The Pectoralis Muscle is a very large triangular 

 muscle, having its origin on the sternum and the 

 cartilages of the ribs and its insertion on the hume- 

 rus. It is made up of the following five por- 

 tions : 



a. A long, narrow superficial division which 

 arises from the manubrium. Part of this is in- 

 serted in the fascia of the fore-leg, and part of it 

 joins one of the shoulder muscles, the cephalo-hu- 

 meral. (Plate IV.) 



b. The next division arises from the raphe in 

 front of the manubrium and from the manubrium 

 and is inserted on the outer side of the deltoid 

 ridge of the humerus. It lies beneath a, and is 

 more or less closely united with c. (Plate IV.) 



c. This division arises from the above mentioned 

 raphe' and from the sternum as far back as the car- 



