6 TOPOGRAPHICAL ANATOMY OF THE 



Dissection. — Clean the surface of the muscles that lie between the 

 ribs, and of the transverse costal muscle that runs obliquely over the 

 sternal end of the first three ribs. 



M. TRANSVERSUS COSTARUM. — The transverse costal muscle is flat 

 and th*n, and arises from the first rib ventral to the scalene tubercle. 

 It passes obliquely in a caudal and ventral direction and ends on the 



Dorsal ramus of thoracic nerve. 



M. niultifidus. 



Dorsal branch of intercostal artery. 



M. longissimus 

 dorsi. 



M. levator costae 



M. iliocostalis. 



Dorsal cutaneous nerve. 

 Fig. 3. — Deep dissection of the Back in the Thoracic Region. 



extremities of the second, third and fourth costal cartilages and the 

 adjacent part of the sternum. 



Mm. intercostales externi. — On each side of the chest there are 

 seventeen external intercostal muscles. Each passes from the caudal 

 border of one rib to the cranial border of the next, its fibres sloping in 

 a caudal and ventral direction. Ventrally the muscles end at the 

 junction of the bony segment of the rib and the costal cartilage. 

 Dorsally each muscle comes into contact with a levator of the rib, from 



