$4 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. 

 Nei've. — Intercostal. 



TRIANGULARIS STERNI. 



Origin. — From superior border of sternum. 

 Insertiofi. — 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. 



