360 



DISSECTION OF THE BACK. 



Fig. 117. 



processes, and removing loose areolar tissue, the thin upper serratus muscle 

 beneath them will be laid bare. 



The splenius and the inferior serratus have been previously exposed by 



the reflection of the trapezius and 

 latissimus. 



* The SERRATI muscles are 

 very thin, and receive their name 

 from their toothed attachment to 

 the ribs. They are two in num- 

 ber, superior and inferior, and 

 have aponeurotic origins from the 

 spines of the vertebra;. 



* The serratus posticus supe- 

 rior (fig. 117, A ) arises from the 

 ligamentum nuchre, and from the 

 spinous processes of the last cer- 

 vical, and two or three upper 

 dorsal vertebrae. The fleshy 

 fibres are inclined down and out, 

 and are inserted by slips into the 

 second, third, and fourth ribs, 

 external to their angles. 



The muscle rests on the sple- 

 nius, and is covered by the rhoin- 

 boideus major. 



* The serratus posticus infe- 

 rior (fig. 116, G ) occupies the 

 lumbar region, and is wider than 

 the preceding muscle. Its apo- 

 neurosis of origin is inseparably 

 united with that of the latissimus 

 dorsi, and with the fascia lumbo- 

 rum, and is connected to the 

 spinous processes of the last two 

 dorsal and first three lumbar ver- 

 tebrae. The fleshy fibres ascend 

 to be inserted into the last four 

 ribs in front of their angles, each 

 successive piece extending further 

 forwards than the one below. 



This muscle lies on the mass of the erector spinae ; and with its tendon 

 the vertebral aponeurosis is united. 



Action. The superior serratus raises the upper ribs, and officiates as an 

 inspiratory muscle ; and the inferior, depressing the lower ribs, becomes an 

 expiratory muscle. Theile supposes the inferior to act indirectly as a 

 muscle of inspiration, because, by fixing the lower ribs, it enables the dia- 

 phragm to contract more effectively. 



* The vertebral aponeurosis is a fibrous expansion, which is spread over 

 the fourth layer of muscles, and confines the erector spina- in the. vertebral 

 groove. 



Inferiorly it is thickened by the tendons of the latissimus and lower 

 serrutus; but it is continued above beneath the splenius, without joining 

 the upper serratus, and blends with the deep fascia of the neck. 



PART OF THE THIRD LAYER OF THE BACK- 

 MUSCLES. 



A. Serratns posticus superior. 



B. Splenius capitis. 

 c. Splenius colli. 



D. Ilio-costalis. 



E. Longissimus dorsi. 

 p. Spinalis dorsi. 



