404 



MYOLOGY 



of which is inserted as above described; the other passes down to the second 

 rib below its origin (Levatores costarum longi). 



The Serratus posterior superior (Senatus posticiis superior) is a thin, quadri- 

 lateral muscle, situated at the upper and back part of the thorax. It arises by 

 a thin and broad aponeurosis from the lower part of the ligamentum nuchae, 

 from the spinous processes of the seventh cervical and upper two or three thoracic 



vertebrae and from the supraspinal liga- 

 ment. Inclining downward and lateral- 

 ward it becomes muscular, and is in- 

 serted, by four fleshy digitations, into 

 the upper borders of the second, third, 

 fourth, and fifth ribs, a little beyond 

 their angles. 



Variations. Increase or decrease in size and 

 number of slips or entire absence. 



The Serratus posterior inferior (Ser- 

 ratus posticus inferior) (Fig. 409) is sit- 

 uated at the junction of the thoracic 

 and lumbar regions: it is of an irreg- 

 ularly quadrilateral form, broader than 

 the preceding, and separated from it by 

 a wide interval. It arises by a thin 

 aponeurosis from the spinous processes 

 of the lower two thoracic and upper two 

 or three lumbar vertebras, and from 

 the supraspinal ligament. Passing 

 obliquely upward and lateral ward, it 

 becomes fleshy, and divides into four 

 flat digitations, which are inserted into 

 the inferior borders of the lower four 

 ribs, a little beyond their angles. The 

 thin aponeurosis of origin is intimately 

 blended with the lumbodorsal fascia, 

 and aponeurosis of the Latissimus dorsi. 



Sternal 

 origin of 

 Diaphragm 



FIG. 390. Posterior surface of sternum and costal 

 cartilages, showing Transversus thoracis. 



Variations. Increase or decrease in size and number of slips or entire absence. 

 Nerves. The muscles of this group are supplied by the intercostal nerves. 



The Diaphragm (Fig. 391) is a dome-shaped musculofibrous septum which 

 separates the thoracic from the abdominal cavity, its convex upper surface forming 

 the floor of the former, and its concave under surface the roof of the latter. Its 

 peripheral part consists of muscular fibers w r hich take origin from the circumference 

 of the thoracic outlet and converge to be inserted into a central tendon. 



The muscular fibers may be grouped according to their origins into three parts 

 sternal, costal, and lumbar. The sternal part arises by two fleshy slips from 

 the back of the xiphoid process; the costal part from the inner surfaces of the car- 

 tilages and adjacent portions of the lower six ribs on either side, interdigitating 

 with the Transversus abdominis; and the lumbar part from aponeurotic arches, 

 named the lumbocostal arches, and from the lumbar vertebrae by two pillars or 

 crura. There are two lumbocostal arches, a medial and a lateral, on either side. 



The Medial Lumbocostal Arch (arcus lumbocostalis medialis [Halleri]; internal 

 arcuate ligament) is a tendinous arch in the fascia covering the upper part of the 

 Psoas major; medially, it is continuous with the lateral tendinous margin of the 

 corresponding crus, and is attached to the side of the body of the first or second 



