524 



DISSECTION OF THE BACK. 



Vertebral 

 aponeu- 

 rosis : 



attach, 

 merits ; 



continua- 

 tion below, 

 and above. 



Muscles of 

 fourth layer. 



Dissection. 



Splenius has 

 two parts : 



one to the 

 neck ; 



the other to 

 the head ; 



relations. 



Use of 



splenius 



eapitis, 



splenius 

 colli. 



Divide 

 splenius, 

 and seek 

 nerves. 



backwards the lower ribs, and prevents their being carried upwards 

 by the contraction of the diaphragm. 



The VERTEBRAL APONEUROSis is a thin fascia which covers the 

 fourth layer of muscles in the thoracic region. Internally it is 

 attached to the spinous processes of the vertebrae. Externally it is 

 fixed to the angles of the ribs ; and in the intervals between the 

 bones it joins the layer of connective tissue covering the intercostal 

 muscles. It is continuous below with the tendon of the serratus 

 posticus inferior, and through this with the superficial layer of the 

 fascia lumborum ; but above, it passes beneath the upper serratus, 

 and blends with the deep interniuscular fascia of the neck. The 

 strongest fibres of the membrane are directed transversely. 



FOURTH LAYER OF MUSCLES. This comprises the splenius 

 muscle and the erector spinse, with its divisions and accessory 

 muscles to the neck. 



Dissection. The upper serratus is to be cut through, the 

 vertebral aponeurosis taken away, and the part of the splenius 

 muscle under the serratus cleaned. In turning outwards the fleshy 

 part of the serratus, slender twigs of the intercostal nerves, which 

 perforate the external intercostal muscle accompanied by small 

 arteries, may be found entering its slips. 



The SPLENIUS MUSCLE (fig. 190) is flat and elongated. Single 

 at its origin, it is divided into two parts, one passing to the 

 head splenius capitis, and the other to the neck splenius colli. 

 It arises from the upper six dorsal and the seventh cervical spines, 

 and from the ligamenturn nuchfe as high as the third cervical 

 vertebra. The fibres are directed upwards and outwards to their 

 insertion. 



The splenius colli (c marked low down on the left side of the figure) 

 is inserted by tendinous slips into the posterior tubercles of the trans- 

 verse processes of the upper two or three cervical vertebrae with, but 

 behind, the attachment of the elevator of the angle of the scapula. 



The splenius capitis (B), much the larger, is inserted into the apex 

 and hinder border of the mastoid process, and into the outer third 

 of the superior curved line of the occipital bone. 



The muscle is situate beneath the trapezius, the rhomboidei, and 

 the serratus superior ; and the insertion into the skull is beneath 

 the sterno-mastoid. The complexus muscle appears above the upper 

 border of the splenius capitis. The splenius represents the pro- 

 longation to the upper cervical vertebrae and head of the outer 

 portion of the erector spinse. 



Action. The cranial parts of the muscles of the two sides will 

 carry the head directly back ; and one will incline and rotate the 

 head to the same side. 



The splenius colli of both sides will bend back the upper cervical 

 vertebrae ; but one muscle will turn the face to the same side, being 

 able to rotate the head by its attachment to the transverse process 

 of the atlas. 



Dissection (fig. 191, p. 527). The splenius is to be detached 

 from the spinous processes, and thrown outwards. In doing this, 



