Fig. 80. Transverse Section through the Middle of the Right Arm. 



A specimen from a series of sections taken from a frozen body. This section 



sliews the under surface of a right upper stump, or the upper surface of a left 



arm. For practical purposes, the former interpretation is to be preferred. 



Note : The relation of the Median Nerve to the Brachial Artery ; the Ulnar 

 Nerve and the Musculo-Spiral Nerve winding round the bone. The External 

 Intermuscular Septum is well displayed; the Internal is not distinctl}' visible in 

 this section. 



The Flexors (Brachialis Anticus, Biceps and Coraco-Brachialis), are separated 

 from the Extensors (Triceps) by the Intermuscular Septa. The Internal Septum 

 runs along the inner border of the Humerus to the Internal Condyle. The External 

 Septum extends from the insertion of the Deltoid Muscle downwards along the 

 outer border of the shaft of the Humerus to the External Cond3'le. The Internal 

 Septum is really the fibrous continuation of the Coraco-Brachialis (which passes 

 in some animals to the Internal Condyle). The enormous Triceps presses these 

 Septa forwards; in this section they are shewn to describe a curve with its con- 

 vexity directed forwards. Both groups of Muscles thus lie in fibrous sheaths, 

 formed by the Fascia of the arm, the Intermuscular Septa and the Periostium. 



Fig. 81. Transverse Section through the Lower Third of the 



Right Arm. 



Section through a right arm hardened in formalin. Interpretation similar to 



that of the section above (Fig. 80). 



Note the differences in shape, size, and position of the various structures, 

 as compared with Fig. 80. Shape of the Humerus, of the Biceps, of the Brachialis 

 Anticus, of the Triceps. — Change in the position of the Musculo-Spiral Nerve 

 which has left the bone, of the Ulnar Nerve which has reached the Internal Inter- 

 muscular Septum etc. In this figure, all the Fasciae are coloured blue. Thus the 

 continuity of the Intermuscular Septa with the Periosteum, at the outer and at 

 the inner border of the Humerus, and with the Deep Fascia is shewn. The latter 

 binds down the muscles and forms thin fascial septa between them; i. e. between 

 Biceps, Brachialis Anticus, Coraco-brachialis, and between the 3 heads of the Triceps. 



The whole arm is enclosed in the Superficial Fascia which is especially 

 strong on the extensor aspect. On the Deep Fascia run, covered by the super- 

 ficial fascia, the Superficial Veins and Nerves. 



