284 



FASCIA AND MUSCLES OF THE HORSE 



pectoral muscles. It is directed obliquely backward and downward, and crosses 

 the lower part of the first three intercostal spaces. 



Origin.— The lateral surface of the first rib, below the scalenus. 



Insertion.— The cartilage of the fourth rib. The aponeurosis usually joins the 

 rectus abdominis. It may reach the fifth rib or the sternum. 



Cariniform cartilage 



Sternal I 



' First rib 



Internal thoracic vessels 



Internal intercostal muscle 



Costal part of 



diaphragm Sternal Transversus 



(cut edge) part of abdominis 



diaphragm (cut) 



Fig. 274. — Dissection of Floor of Thorax of Horse. 

 The ribs have been sawn off near their sternal ends and the diaphragm and transversus abdominis cut off close to their 



attachment. 

 1, Eighth rib; 2, 3, cartilages of ninth and tenth ribs; 4, xiphoid cartilage; 5, apex of pericardium. 



Action. — It may assist in inspiration or concur with the rectus abdominis. 

 Relations. — Superficially, the deep pectoral muscles; deeply, the intercostal 

 muscles and the ribs. 



Blood-supply. — Internal and external thoracic arteries. 

 Nerve-supply. — Intercostal nerves. 



