64 EQUINE ANATOMY. 



SUPERCOSTALS. 



Origin. From transverse processes of dorsal vertebrae. 

 Insertion. External surface of one or two ribs below. 

 Action. Draws ribs forward in inspiration. 

 Nerve. Superior dorsal. 



SERRATUS MAGNUS. 



Origin. External surface of first eight ribs. 

 Insertion. Anterior and posterior triangular surfaces of scapula 

 and subscapularis. 



Action. Acts to support body as a girdle or depresses scapula. 

 Nerve. Superior thoracic. 



TRANSVERSE COSTAL. 



Origin. External face of first rib. 

 Insertion. Fourth costal cartilage and sternum. 

 Action. Raises ribs and enlarges thorax. 

 Nerve. Intercostal. 



TRIANGULARIS STERNI. 



Origin. From superior border of sternum. 

 Insertion. Cartilages of true ribs except first. 

 Action. Expiratory muscle by depressing cartilages. 

 Nerve. Intercostal. 



DIAPHRAGM. 



The muscular partition between the thoracic and abdominal 

 cavities. 



Origin. By right and left pillars from lumbar vertebrae, con- 

 founded with inferior common ligament of the spine. (Between 

 two pillars pass posterior aorta and thoracic duct.) From xiphoid 

 appendix of sternum and anterior extremities of last twelve ribs. 



Insertion. Phrenic centre, dividing into right and left leaflets. 



RELATIONS. Anteriorly, with pleurae and lungs; posteriorly, 

 peritoneum, stomach, liver, colon and spleen. 



Openings. Behind for aorta and thoracic duct; in right leaflet 

 for vena cava; in right pillar for oesophagus. 



Nerves. Phrenic. 



Action. Muscle of respiration. 



