232 DORSAL MUSCLES OF THE TRUNK. 



tliin ; they afford a delicate but firm covering to the muscles of the thumb 

 and little finger respectively. The central portion is one of the strongest 

 fascise of the body. Occupying the interval between the thenar and 

 hypothenar eminences and expanding towards the fingers, it has a somewhat 

 triangular or fan-like form. The narrow end of the fascia, thicker than any 

 other part, and composed of close parallel fibres, is connected by its deep 

 surface with the anterior annular ligament, and is continuous superiorly 

 with the tendon of the palrnaris longus, when that muscle is present ; the 

 broader portion, becoming thinner and flatter as it advances towards the 

 fingers, has a much more irregular and interlaced texture, and adheres 

 more closely to the skin of the palm. Near the lower part of the palm it 

 separates into four processes, each of which again subdivides iuto two slips 

 next the root of a corresponding finger; and the bundles of fibres thus 

 separated, dipping one on each side of the flexor tendons belonging to the 

 finger, are attached to the margins of the metacarpal bone and to the trans- 

 verse ligament which binds the metacarpal bones to each other. From the 

 centre of each process longitudinal fibres are continued to the skin as far 

 forward as the root of the finger. These digital processes of the palmar 

 fascia are held together by irregular transverse fibres, which lie immediately 

 under the skin, and serve to give great additional strength at the points of 

 divergence. 



MUSCLES OF THE TRUNK. 



The muscles passing between the trunk and the upper limb having been 

 already described, those which belong exclusively to the trunk itself will now 

 be treated of under the three divisions of, 1. Dorsal muscles, extending 

 throughout the whole length ; 2. Thoracic muscles, including the 

 diaphragm ; and 3. Abdominal and Perineal muscles. 



DORSAL MUSCLES OF THE TRUNK (MUSCLES OF THE BACK). 



The muscles to be described under the above head, taken as a whole, 

 occupy more or less deeply the hollow between the entire middle line of the 

 vertebral spines and the prominences formed towards the sides by the 

 mastoid processes, the transverse cervical processes, the most projecting 

 parts of the ribs, and the crest of the ilium, and they extend from the superior 

 curved line of the occipital bone to the lower part of the sacrum. Some 

 consist of comparatively limited portions of muscular substance, and occupy 

 only certain parts of the extensive region now referred to ; others extend 

 either continuously or by the serial repetition of similar fasciculi, through- 

 out the greater part of it. These muscles, together with those in the same 

 region which belong more properly to the upper limb, have been frequently 

 described as constituting six successive layers ; but the limits of several of 

 these layers do not present very marked natural planes of separation, and 

 it will be sufficient for the purpose of description to arrange those which 

 fall properly within the present section, according to the main characteristics 

 of their form and position, into the following groups: viz., a, the posterior 

 serrati muscles ; 6, the splenius and long erectors of the spine ; c, the 

 complex us and transverse spinales ; d, the iuterspiuales and intertrans- 

 versales ; e, the short cranio-vertebral muscles. Of these muscles those 

 included in the first two groups may be considered as having their fibres 

 passing outwards from the middle ; those in the third group as having 

 their fibres passing inwards ; those of the fourth group as having their fibres 



