THE UPPER LIMB 411 



those of the inner four metacarpo-phalangeal joints, namely, two 

 lateral, and an anterior fibrous plate, the extensor tendon taking the 

 place of a dorsal ligament. Each joint is provided with a sjTiovial 

 membrane, and the arterial and nerve supply are derived from the 

 digital arteries and nerves. Each of the inner four fingers has two 

 interphalangeal joints, but the thumb, being destitute of a middle 

 phalanx, has only one, and its dorsal hgament is represented by 

 the tendon of the extensor longus pollicis, whilst its fibrous plate 

 is grooved by the tendon of the flexor longus pollicis. 



Movements. — The only movements allowed are flexion and extension, the 

 former being very free. 



Joints with Interarticular Fibro-cartilages. — ^The joints of the 

 upper Umb which have interarticular fibro-cartilages are as follows : 



1. The stemo-clavicular joint. 



2. The acromio-clavicular joint (inconstant). 



3. The triangular fibro-cartilage of the inferior radio-ulnar 

 articulation is to be regarded as an interarticular fibro-cartilage 

 between the ulna and cuneiform bone at the radio-carpal joint. 



The shoulder-joint has a circumferential fibro-cartilage, namely, 

 the glenoid ligament. 



GUIDE TO THE UPPER LIMB. 



The Back. — To remove the skin, the following incisions may be made : one 

 along the middle line from the seventh cervical spine to the second sacral spine ; 

 another from the upper end of this incision outwards to the acromion process, 

 and thence downvsards over the back of the shoulder in a curved manner to 

 meet the posterior fold of the axilla ; and a third from the lower end of the 

 mesial incision outwards along the iUac crest. The cutaneous nerves will be 

 found near the spines of the upper six thoracic vertebrae and near the angles 

 of the lower six ribs. Tliree branches from the first three lumbar nerves are 

 fto be shown descending over the ihaic crest to the gluteal region. 



The trapezius muscle is to be cleaned, and, in doing so, as well as in the deep 

 ^Stages of this dissection, it is advisable that the dissector of the upper Umb 

 'lould work in concert with the dissector of the head. The spinal accessory 

 serve will be found passing beneath the anterior border of the trapezius. 

 1.Tie latissimus dorsi is next to be cleaned, and turning backwards round its 

 iter border will be found the posterior ofisets of the lateral cutaneous branches 

 Df the intercostal nerves. Between the contiguous borders of the latissimus 

 iorsi and obhquus extemus abdominis, just above the centre of the iUac crest, 

 triangle of Petit is to be shown. The region between the trapezius, 

 itissimus dorsi, and base of the scapula, and the parts contained therein, are 

 to be studied. The trapezius is to be divided about i inch from the spines of 

 'lie vertebrae, and the spinal accessory nerve, with branches of the thnrd and 

 lourth cervical nerves, and the superficial cervical artery, are to be dissected on 

 Its deep surface. The latissimus dorsi is to be divided by an incision carried 

 iownwards from its upper border about 3 inches from the spines of the vertebrae 

 the back part of the iliac crest internal to the iUac origin of the muscle, 

 fso as to leave undisturbed its sUps of origin from the lower three or four ribs, 

 well as its ihac origin. In reflecting inwards the inner portion of the muscle 

 re is to be taken not to injure the serratus posticus inferior, and, in turning 

 Jutwards the outer portion, the serratus magnus is not to be interfered with. 

 The levator anguli scapulae and rhomboid muscles are to be dissected, and 

 the nerve to the rhomboids is to be looked for deeply between these two 



