MUSCLES OF THE BACK. 207 



anterior intertransversales are thin, and occupy only part of the space be- 

 tween the transverse processes. Analogues of posterior intertransversales 

 exist in the form of small muscular fasciculi (interobliqui) extended be- 

 tween the rudimentary posterior transverse processes of the lumbar ver- 

 tebrae. 



With regard to the origin and insertion of the muscles of the back, the 

 student should be informed, that no regularity attends their attachments. 

 At the best, a knowledge of their exact connexions, even were it possible 

 to retain it, would be but a barren information, if not absolutely injurious, 

 as tending to exclude more valuable learning. I have therefore endea- 

 voured to arrange a plan, by which they may be more easily recollected, 

 by placing them in a tabular form (p. 208), that the student may see, at 

 a single glance, the origin and insertion of each, and compare the natural 

 grouping and similarity of attachments of the various layers. In this 

 manner also their actions will be better comprehended, and learnt with 

 greater facility. 



Actions. The upper fibres of the trapezius draw the shoulder upwards 

 and backwards ; the middle fibres, directly backwards ; and the lower 

 downwards and backwards. The lower fibres also act by producing ro- 

 tation of the scapula upon the chest. If the shoulder be fixed the upper 

 fibres will flex the spine towards the corresponding side. The latissimus 

 dorsi is a muscle of the arm, drawing it backwards and downwards, and 

 at the same time rotating it inwards ; if the arm be fixed, the latissimus 

 dorsi will draw the spine to that side, and, raising the lower ribs, be an 

 inspiratory muscle ; and if both arms be fixed, the two muscles will draw 

 the whole trunk forwards, as in climbing or walking on crutches. The 

 levator anguli scapulae lifts the upper angle of the scapula, and with it the 

 entire shoulder, and the rhomboidei carry the scapula and shoulder up- 

 wards and backwards. 



In examining the following table, the student will observe the constant 

 recurrence of the number four in the origin and insertion of the muscles. 

 Sometimes the four occurs at the top or bottom of a region of the spine, 

 and frequently includes a part of two regions, and takes two from each, 

 as in the case of the serrati. Again, he will perceive that the muscles of 

 the upper half of the table take their origin from spinous processes, and 

 pass outwards to transverse, whereas the lower half arise mostly from 

 transverse processes. To the student, t ,en, we commit these reflections, 

 and leave it to the peculiar tenor of his own mind to make such arrange- 

 ments as will be best retained by his memory. 



The serrati are respiratory muscles acting in opposition to each other, 

 the serratus posticus superior drawing the ribs upwards, and thereby ex- 

 panding the chest ; and the inferior drawing the lower ribs downwards 

 and diminishing the cavity of the chest. The former is an inspiratory, 

 the latter an expiratory muscle. The splenii muscles of one side draw 

 the vertebral column backwards and to one side, and rotate the head to- 

 wards the corresponding shoulder. The muscles of opposite sides, acting 

 together, will draw the head directly backwards. They are the natural 

 antagonists of the sterno-mastoid muscles. 



The sacro-lumbalis with its accessory muscle, the longissimus dorsi, and 

 spinalis dorsi, are known by the general term of erectores spina, which 

 sufficiently expresses their action. They keep the spine supported in the 

 vertical position by their broad origin from below, and by means of theii 



