498 ^ MANUAL OF ANATOMY 



rounded by a coloured circle, called the areola. The exact position 

 of the nipple is subject to variation. As a rule it may be said to 

 lie over the fourth intercostal space about 4 inches from the mid- 

 sternal line, but in corpulent persons, and in females with pendulous 

 mammae, it is lower in position. Along the middle line the sternum 

 can readily be made out, and about 2 inches below its upper border 

 the transverse ridge, called the sternal angle, may be felt, which is 

 the guide to the second costal cartilage at. either side. Above the 

 centre of the upper border of the sternum is a depression, known 

 as the jugular fossa. Below the lower border of the mesosternum 

 there is the infrasternal depression, which is situated between the 

 seventh pair of costal cartilages, where it lies over the meta- 

 sternum. 



Cutaneous Nerves. — ^These nerves are arranged in three groups — 

 descending, anterior, and lateral. 



The descending nerves are branches of the cervical plexus, and 

 are derived from the third and fourth cervical nerves. They are 

 three in number — suprasternal or internal, supraclavicular or middle, 

 and supra- acromial or external — and, as they descend, they lie 

 beneath the platysma myoides. The suprasternal nerve crosses the 

 inner end of the clavicle, and its branches are distributed to the sub- 

 jacent integument, as well as to that over the upper part of the 

 sternmn. The supraclavicular nerve crosses the centre of the bone, 

 and its branches have a fairly wide distribution to the pectoral in- 

 tegument. The supra-aeromial nerve crosses the outer end of the 

 clavicle, and its branches are distributed to the integument over the 

 upper half of the deltoid. 



The anterior cutaneous nerves are the terminal branches of the 

 upper six intercostal nerves, and they pierce the pectoralis major 

 close to the sternum. They furnish small twigs to the integument 

 over that bone, but the principal part of each nerve takes an out- 

 ward course and supplies the pectoral integument. The branch of 

 the first nerve is sometimes absent. 



The lateral cutaneous nerves are branches of the intercostal 

 nerves from the third to the sixth inclusive. The first inter- 

 costal nerve gives no lateral cutaneous branch. The lateral 

 cutaneous of the second intercostal nerve is undivided, and crosses 

 the axillary space to the brachial region, under the name of inter- 

 costo-humeral. The succeeding lateral cutaneous nerves emerge 

 from their intercostal spaces by piercing the external intercostal 

 muscles not far from the lower border of the pectoralis major. 

 Each then divides into an anterior and a posterior branch, which 

 pass out between the digitations of the serratus magnus, being 

 separated from each other by a slight interval. The anterior 

 branches wind round the lower border of the pectoralis major to 

 supply the pectoral integument, whilst the posterior branches pass 

 backwards to supply the integument over the anterior border of the 

 latissimus dorsi. 



The anterior aad lateral cutaneous nerves are accompanied by 



