10 TOPOGRAPHICAL ANATOMY OF THE 



dominal muscle, aud each divides into a small dorsal and a larger ventral 

 branch. The latter supply filaments to the skin and the external 

 oblique muscle. The lateral cutaneous branches of some of the last 

 intercostal nerves are distributed in the wall of the abdomen. 



Aa. lumkales. — Lumbar arteries behave, in the main, in the same 

 manner as do the intercostal arteries. In the present dissection it is 

 only necessary to note that their dorsal branches supply the muscles 

 and skin of the back in the lumbar region. 



Nn. lumbales. — Like the thoracic nerves, these divide into dorsal 

 and ventral branches. They are examined in detail during the dis- 

 section of the abdomen. It has already been noted that the dorsal 

 branches furnish cutaneous nerves that pierce the lumbar portion of the 

 longissimus dorsi muscle. 



Dissection. — The intercostal muscles should be carefully removed 

 from one or two interspaces. This will reveal that part of the 

 endothoracic fascia that lines the lateral wall of the chest. 



The endothoracic fascia (Fascia endothoracica). — The endothor- 

 acic ^ fascia forms a thin elastic lining to the wall of the chest. Its inner 

 face is covered by and gives support to the parietal part of the pleura. 

 In the mid-dorsal line the fascia is connected with the aorta and the 

 other large blood vessels in this neighbourhood, while in the sternal 

 region it is continuous with the fibrous layer of the pericardium. 



At the present moment, only those portions of the endothoracic 

 fascia that bridge the intervals between the ribs are exposed. An 

 examination here will show tliat the fascial fibres run, for the most part, 

 from the border of one rib to the adjacent margin of the next ; and later, 

 when portions of the ribs are removed, it will be possible to determine 

 that the fascia is stronger where it crosses the intercostal spaces than it 

 is where it is applied to the inner surface of the ribs themselves. And 

 at a still later stage of the dissection, it will be found that the fascia is 

 very thin where it covers the cranial surface of the diaphragm. 



The thoracic cavity (Cavum thoracis). — It is necessary that the 

 dissector should have some general idea of the thoracic cavity and the 

 organs contained therein before he proceeds to their examination. The 

 thorax is a cavity with a bony wall formed by the thoracic vertebrae, 

 the ribs and the sternum. In form it resembles a laterally flattened 

 cone, with a sloping base bounded by the diaphragm, which forms a thin 

 muscular and tendinous partition between the cavity of the thorax and 

 that of the abdomen. It is important to remember that, the diaphragm 

 being markedly concave when viewed from the abdominal aspect, the 



1 ivbov (endon) [Gr.], within, ©wpaf (thorax) [Gr.], a breastplate, cuirass, corslet, 

 the part covered by the breastplate, the chest. 



