DisTi:ii;rrio\ or nil-: CUTANEOUS \ritv i-:x 



cervical nerves, forming with them a loop, the aiisa hyponlossi (fig. 707). The 

 ansa hypoglossi may be placed at any level from a point immediately below the 



;>ital artery to about lour c-eiitimet re.- above the .-ternum. A twig to the ante- 

 rior belly of the omo-hyoid arises from the descendens hypoulossi in the upper part 

 of its course. The nerves which supply the sterno-hyoid, sterno-thyreoid, and 

 posterior belly of the omo-hyoid are given off l>y the ansa liyjx^lossi. Twins from 

 the first two nerve- pa-- downwards in the muscles behind the manubrium sterni 

 and in rare cases communicate with the phrenic nerve within the thorax. The 

 nerve to the posterior belly of the omo-hyoid runs in a loop of the cervical fascia 

 below the central tendon of the muscle. 



(1)) The nerve to the thyreo-hyoid is given off near the tip of the great cornu 

 of the hyoid bone, and runs obliquely downwards and inwards to reach the muscle. 



(3) The true hypoglossal branches, the rami linguales, supply the stylo- 

 glossus, hyo-glossus, genio-glossus, the genio-hyoid, and the intrinsic muscular fibres 

 of the tongue. 



The nerve to the stylo-glossus is given off near the posterior border of the 

 hyo-glossus. It pierces the stylo-glossus, and its fibres pursue a more or less re- 

 current course within the muscle. 



The nerves to the hyo-glossus are several twigs which are supplied to the muscle 

 as the hypoglossal nerve; crosses it. 



The nerves to the genio-glossus and genio-hyoid arise under cover of the 

 mylo-hyoid in common with the terminal branches to the intrinsic muscles of the 

 tongue. They communicate freely with branches of the lingual, forming long 

 loops which lie on the genio-glossus. From these loops twigs pass into the genio- 

 glossus and into the muscular substance of the tongue. It is not improbable that the 

 fibres to the genio-hyoid are really derived from the cervical net- 

 Central Connections. The nucleus of oripin of the, hyppglossus is associated with the som- 

 a-sthcfic Mi-en (operculum) of the cortex cerebri of the opposite side by the pyramidal fibres, and 

 it is connected with the sensory nuclei (nuclei of termination) of other cranial nerves by the 

 medial longitudinal fasciculus. 



THE DISTRIBUTION OF THE CUTANEOUS BRANCHES OF THE SEN- 

 SORY AND MIXED CRANIAL AND SPINAL NERVES 



The cutaneous filaments of the sensory and mixed nerves are distributed to 

 definite regions of the surface of the body which are known as 'cutaneous areas.' 

 Each cutaneous area has one special nerve of supply and the central part of the 

 area receives that nerve alone, but wherever the borders of two areas meet they 

 reciprocally overlap, therefore eacr; margin of every cutaneous area has two nerves 

 of supply, its own nerve and that of an adjacent area, and of these, sometimes one 

 and sometimes the other preponderates. 



THE CUTANEOUS AREAS OF THE SCALP 



The limits of the cutaneous areas in the scalp region are indicated in figs. 708, 

 710, but in general terms it may be said that the skin of t he scalp in front of the pinna 

 is supplied by four cutaneous nerves, viz., the mesial part by the supratrochlear 

 and the supra-orbital branches of the first division of the trigeminus, and the lateral 

 part by the temporal branch of the second division, and the auriculo-temporal branch 

 of the third division of the same nerve. 



The portion of the scalp behind the pinna also receives four cutaneous nerve.-: 

 laterally it is supplied by the great auricular and small occipital branches of the 

 cervical plexus which contain filaments from the second and third cervical net 

 and medially it receives the great and smallest occipital nerves which are derived 

 from the internal branches of the posterior primary divisions of the second and 

 third cervical nerves respectively. 



THK CUTANEOUS AKK\S OF THI: F\n; 



With the exception of the skin over the posterior part of the masseter muscle the 

 whole of the skin of the face is supplied by the branches of the trigeminus. The 



