OSTEOLOGY. 61 



the last bone, decreasing in size posteriorly to form tlie 

 neck, subsequently again expanded in forming an aiypendix 

 portion. To its under surface are attached the abdominal 

 oblique and rectus muscles, also pectoralis magnus, to the 

 upper surface the diaphragm and trans versalis abdominis 

 and the fibrous pericardium. The sternum thus presents three 

 surfaces and two extremities. The anterior extremity is the 

 prow of the carinif orm cartilage ; to it sterno-maxillaris 

 and sterno-thyro-hyoideus are attached. The jjosfer /or ex- 

 tremity is formed by the ensiform cartilage. The lateral 

 surfaces anteriorly give attachment to pectoralis anticus, 

 posteriorly to pectoralis magnus and trausversus. The 

 inferior margin is anteriorly smooth and rounded ; it here 

 presents a spurious bursa, over which pectoralis traus- 

 versus plays. The tipper surface is slightly concave, both, 

 longitudinally and transversely. Centrally it affords at- 

 tachment to the mediastinum. Anteriorly the thymus 

 gland rests on it, posteriorly the fibrous pericardium is 

 attached. Laterally it presents the articulatory surfaces 

 for the inferior extremities of the sterno-costal cartilages, 

 and internally placed to this the internal thoracic artery 

 runs from before backwards, with its accompanying vein. 

 The first- sterno-costal cartilage articulates with the sternum 

 just in front of the first bone, the second, third, fourth, 

 and fifth with the intervals between the following bones, 

 the sixth with the fifth bone, the seventh and eighth witk 

 the last. 



BONES OF THE FORE LIMB. 



The SCAPULA is a flat triangular bone, placed on the 

 antero-lateral part of the thorax, having its apex inferiorly 

 opposite the first rib, its base extending oblicjuely down- 

 wards as far as the angle of the sixth rib. A. fiat bone is 

 required in this position to aftbrd sufficient surface for 

 attachment of the large muscles which connect the fore 

 limb to the trunk, for in the horse two bones (coracoid and 

 clavicle) which perform this function in many other animals 

 are rudimentary. It presents two surfaces, three borders, 

 and three angles. The anterior border is superiorly convex 

 and roughened, inferiorly concave and smooth, and at its 

 extreme inferior part presents a large roughened process, 

 coracoid (a rudiment of a distinct bone). This process 

 externally presents, superiorly a groove for a blood-vessel 



