THORACIC WALL- 5 



In addition to the osseous and cartilaginous framework, 

 the walls of the thorax are built up partly of muscles, and 

 partly of membranes, and in connection with those there are 

 numerous nerves and blood-vessels. 



External intercostals. 

 I Internal intercostals. 

 Muscles, . ^Transversithoracis. 



Membranes, 



Subcostals. 



Anterior intercostal membranes. 



Posterior intercostal membranes. 



Pleural membranes (parietal parts). 



{Intercostal nerves. 

 Aortic intercostal arteries. 

 Superior intercostal arteries. 

 Internal mammary arteries. 



As the thorax may be the first " part " that the student 

 dissects it is important, before he commences work, that 

 he should have a clear idea of the constitution of a typical 

 spinal nerve. Every spinal nerve is attached to the spinal 

 medulla (spinal cord) by two roots, an anterior root and a 

 posterior root (Fig. 2). The posterior root has a swelling upon 

 it which is called a ganglion ; the anterior root is non- 

 ganglionated. As the roots leave the vertebral canal 

 through an intervertebral foramen they unite to form a 

 trunk. Immediately after its exit from the intervertebral 

 foramen the trunk divides into an anterior ramus and a 

 posterior ramus (Fig. 2), of which the anterior ramus is, 

 with few exceptions, much the larger. Each posterior ramus 

 divides into a medial branch and a lateral branch. Each 

 anterior ramus divides into a lateral branch and an anterior 

 or ventral branch. 



Every anterior root consists of nerve fibres which spring 

 from nerve cells in the spinal medulla and pass to the muscle 

 fibres of various muscles. They carry motor impulses to the 

 muscles. Each posterior root consists of nerve fibres passing 

 to and from the nerve cells of the ganglion of the posterior 

 root. The posterior root fibres carry sensory impulses, such 

 as cold, heat, pain, etc. The sensory impulses pass through 

 the cells of the ganglion of the posterior root and then 

 onwards to the spinal medulla. 



The trunk 'of every spinal nerve, therefore, contains both 

 motor or efferent and sensoty or afferent nerve fibres, and the 

 posterior and anterior rami into which it divides also contain 

 both sets of fibres. The branches of the rami may contain 



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