1406 



CLINICAL AND TOPOGRAPHICAL ANATOMY 



Triangle of Petit. — This small space lies above the crest of the ilium, at about 

 its centre, bounded bj' the anterior edge of the latissimus behind and the posterior 

 border of the external oblique, in front. Through this gap, when the muscles 

 are weak, a lumbar abscess occasionally, and very rarely, a lumbar hernia, may 

 appear. 



Origin of spinal nerves. — It is very important to remember the relations of 

 these to the vertebral spines, in determining the results of disease or injury of the 

 cord and the parts thereby affected. The above relations may be given briefly 

 as follows : — 



The origins of the eight cervical nerves correspond to the cord between the 

 occiput and the sixth cervical spine. The upper six thoracic come off between 



Fig. 1126. — Chief Arterial Anastomoses on the Scapula. 



(From a dissection in the Hunter ian Museum.) 



Supra-spinatus Transverse scapular artery 



Descending branch of transversa colli artery I I Infra-spinatus 



Rhomboideus minor / I I Triceps, cut 



Levator scapulae / / \ \ \ \ 



Deltoid, insertion 



Deltoid 



Trapezius 



Rhomboideus major 



Teres major 



Deltoid 



Teres major, insertion 



Circumflex scapular artery Posterior circumflex artery 



the above spine and that of the fifth thoracic vertebra. The origins of the 

 lower six thoracic nerves correspond to the interval between the fourth and the 

 tenth thoracic spines. The five lumbar arise opposite the eleventh and twelfth 

 thoracic spines; and the origins of the five sacral correspond to the first lumbar 

 spines. The diagram and table (fig. 1124), arranged by Dr. Gowers from 

 anatomical and j^athological data, sfiow the relations of the origins of the nerves 

 to tiieir exits from the vertebral canal, and the regions supplied by each. 



Scapula, its muscles and arterial anastomoses.^ — ^Amongst the landmarks 

 in the back, the student should be careful to trace the angles and borders of the 

 scapula as far as these are accessible. The upper border is the one most thickly 

 covered. With the hands hanging down, the upper (medial) angle corresponds 

 to the upper border of the second rib; the lower angle to the seventh intercostal 

 space; and the root of the spine of the scapula to the interval between the third 

 and fourth thoracic spines. 



