52 TOPOGRAPHICAL ANATOMY OF THE 



thoracic and pectoral muscles, as well as the skin in the neighbourhood 

 of the sternum, and anastomose with branches of the external thoracic 

 artery. 



(3) Aa. thymicce. — Thymic arteries are, naturally, only possible of 

 demonstration in young animals before the disappearance of the 

 th3Mnus. 



(4) A. ])erica7-diacophrenica.— A very small pericardiaco-phrenic 

 artery may sometimes be found arising on a level with the fourth rib 

 and ending in the pericardium, mediastinum and (possibly) the sternal 

 part of the diaphragm. 



(5) A. viiisculopJirenica . — The musculo-phrenic artery follows the 

 sternal attachment of the diaphrai^m — at first on its thoracic side, and 

 afterwards on its abdominal aspect — as far as the cartilage of the last 

 rib. It furnishes branches that supply part of the diaphragm, the 

 intercostal muscles, and the transverse muscle of the abdomen. 

 Branches (rami intercostales) also anastomose with the intercostal 

 arteries. 



(6) A. epigastrica cranialis. — The cranial epigastric artery, from 

 its size and the direction of its course, may be regarded as the direct 

 continuation of the internal thoracic. It quickly leaves the thorax by 

 passing between the ninth costal cartilage and the xiphoid process of 

 the sternum. The rest of its course belongs to the abdomen, where it 

 is found on the dorsal face of the rectus abdominis muscle. 



V. THORACICA INTERNA. — The internal thoracic vein lies medial to 

 the artery, and is a close satellite of this vessel. It ends by joining the 

 cranial vena cava at the first rib. 



Dissection.—- The joints connected with the costal cartilages and 

 sternum should now be exposed by clearing away all the remains of 

 muscles, &c. 



CosTO-CHONDRAL - ARTICULATIONS (Articulationes costochondrales). 

 — The vertebral end of each costal cartilage is received into a shallow 

 pit at the extremity of a rib-bone, the periosteum of the rib being 

 continuous with the perichondrium of the cartilage. 



Sterno-costal articulations (Articulationes sternocostales). — 

 The cartilages of the sternal ribs are received into fovea ranged along 

 the border of the sternum. Since movement is necessary in these joints, 

 each is provided with a strong joint-capsule (capsula articularis) enclos- 

 ing a joint-cavity and furnished with a synovial lining. It will be 

 noticed that the cartilaginous extremities of the first pair of ribs are 

 received into a common fovea, and enclosed in a common joint-capsule. 



' Costa [L.], a rib. \bvbpo% (chondros) [Gr.], cartilage. 



