1018 THE NERVOUS SYSTEM 



The dorsal nerve of the penis runs forward in Alcock's canal above the 

 internal pudic artery. It pierces the base of the uro-genital trigone, continues 

 forward between the layers of the trigone, embedded in the fibres of the con- 

 strictor uretlirae, and it gradually passes to the lateral side of the internal pudic 

 artery. A short distance below the pudic arch it pierces the anterior layer of the 

 uro-genital trigone, gives a branch to the corpus cavernosum penis, passes 

 forward between that structure and the bone, and turns downward on the dorsum 

 of the penis, passing between the layers of the fundiform (suspensory) ligament 

 and along the outer side of the dorsal artery of the penis. It supplies the skin 

 of the dorsum of the penis, and, having given branches to the prepuce, it breaks 

 up into terminal filaments which are distributed to the glans penis. 



The dorsal nerve of the clitoris is much smaller than the dorsal nerve of the 

 penis to which it corresponds. Is is distributed to the clitories. 



THE COCCYGEAL PLEXUS 



This plexus is frequently, and with some reason, considered as a subdivision of 

 the pudendal plexus, and sometimes it is described with the coccygeal nerves. 

 It is formed chiefly by the anterior division of the fifth sacral nerve and the 

 coccygeal nerve, but it receives a small filament from the anterior division of the 

 fourth sacral nerve (figs. 765, 769). These constituents unite to form plexiform 

 cords lying on either side of the coccyx. From these cords arise the ano-coccygeal 

 nerves, which pierce the sacro-tuberous (great sacro-sciatic) ligament and supply 

 the skin in the neighbourhood of the coccyx. 



III. THE DISTRIBUTION OF THE CUTANEOUS BRANCHES 



OF THE SENSORY 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 each margin of every cutaneous area has two 

 nerves of supply, its own nerve and that of an adjacent area, and of these, some- 

 times 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. 774, 776, but 

 in general terms it may be said that the skin of the 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 ophthalrnic division of the trigeminus, and the lateral part by the temporal branch of the 

 maxillary division, and the auriculo-temporal branch of the mandibular division of the same 

 nerve. 



The portion of the scalp behind the pinna also receives four cutaneous nerves; laterally it 

 is suppUed by the great auricular and small occipital branches of the cervical plexus which 

 contain filaments from the second and third cervical nerves, 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. 



The Cutaneous Areas of the Face 



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

 of the skin of the face is sujjplied by the l)ranches of the trigeminus. The nose is supplied 

 medially by the supratrochlear, the iiifratrochlcar, and the nasal branches of the ophthalmic 

 division, and hiterally by the infra-orbital briincih of the maxillary division. The upper eyehd 

 is supplied l)y the .supratrochlear, the supra-fjrbital, and the lacrimal branches of the ophthal- 

 mic division; the lower eyelid by the infratrochlear branch of the ophthalmic division and 

 by the infra-orbital and the zygomatico-facial (malar) branches of the maxillary division. 

 The skin over the upper jaw and the zygomatic (malar) bone is supplied by the infra-orbital 

 and zygomatico-facial branches of the maxillary division, that over the buccinator by the buccal 

 branch of the mandibular division, and that over the lower jaw, from in front backward, by 

 the mental, buccal, and auricuIo-tcmpDrMl branches of the mandibular division, except a small 

 part near the posterior border which receives its sui)i)ly from tlH> great auricular nerve. 



