176 EHOMBOIDEI SERRATI. 



The rhomboideus major arises from the spinous processes of the 

 four upper dorsal vertebrae and from the supra-spinous ligament ; it 

 is inserted into the posterior border of the scapula as far as its 

 inferior angle. The upper and middle portion of the insertion is 

 effected by means of a tendinous arch. 



Relations. By their superficial surface the two rhomboid mus- 

 cles are in relation with the trapezius, and the rhomboideus major 

 with the latissimus dorsi and integument. By their deep surface 

 they cover in the serratus posticus superior, part of the erector 

 spinae, the intercostal muscles and ribs. 



Third Layer. 



Dissection. The third layer consists of muscles which arise from 

 the spinous processes of the vertebral column, and pass outwards. 

 It is brought into view by dividing the levator anguli scapulae near 

 its insertion, and reflecting the two rhomboid muscles upwards 

 from their insertion into the scapula. The latter should be removed 

 altogether. 



The serratus posticus superior is situated at the upper part of the 

 thorax ; it arises from the ligamentum nuchse, and from the spinous 

 process of the last cervical and two upper dorsal vertebrae ; it is 

 inserted by four serrations into the upper border of the second, 

 third, fourth, and fifth ribs. 



Relations. By its superficial surface with the trapezius, rhom- 

 boideus major and minor, and serratus magnus. By its deep sur- 

 face with the splenius, the upper part of the erector spmse, the 

 intercostal muscles and ribs. 



The serratus posticus inferior arises from the spinous processes of 

 the two last dorsal and two upper lumbar vertebras, and is inserted 

 by four serrations into the lower border of the four lower ribs. 



Relations. By its superficial surface with the latissimus dorsi, its 

 tendinous origin being inseparably connected with the aponeurosis of 

 that muscle. By its deep surface with the aponeurosis of the obli- 

 quus internus, with which it is also closely adherent ; with the 

 erector spina3, the intercostal muscles and lower ribs. The upper 

 border is continuous with a thin tendinous layer, the vertebral 

 aponeurosis. This aponeurosis consists of longitudinal and trans- 

 verse fibres, and extends the whole length of the thoracic region. 

 It is attached mesially to the spinous processes of the dorsal verte- 

 bras, and externally to the angles of the ribs ; superiorly it is con- 

 tinued upwards beneath the serratus posticus superior, with the 

 lower border of which it is sometimes connected. It serves to bind 

 down the erector spinse, and separates it from the superficial 

 muscles. 



The serratus posticus superior must be removed from its origin 

 arid turned outwards, to bring into view the whole extent of the 

 splenius muscle. 



The splenius muscle is single at its origin, but divides soon after 

 into two portions, which are destined to distinct insertions. It 



