778 TSE NEBVUS. 



largest, descends between the two priucipal digits, wliere it bifurcates; above, it gives a 

 Ijranch to the internal digit. 



Caenivoba. — In these animals, the lumbo-sacral plexus is formed by the last four 

 lumbar and the first two sacral. 



Tlie crural and obturator nerves, which arise from the fourth, fifth, and sixth lumbar 

 nerves, ofier nothing particular in their disposition. 



The internal saphenous branch is as long as in the Pig ; it passes to the internal face 

 of the tarsus, lies alongside the fourth metatarsal bone, and forms the internal dorsal 

 collateral of the fourth toe. 



The great sciatic may be described as having, as in Man, two terminal branches 

 which separate a little above the posterior face of the femoro-tibial articulation. The 

 external popliteal nerve passes to the surface of the external gastrocnemius, enters 

 between the common long flexor of the toes and the long lateral peroneal muscle, 

 where it bifurcates. The musculo-cutaneous branch descends beneath the latter muscle 

 to the lower third of the leg, when it becomes superficial, and, accompanied by a vein, 

 is lodged in the interspace between that muscle and the anterior tibial ; it passes in 

 front of the tarsus, and reaches the upper part of the metatarsus, where it divides into 

 three divisions. It must be mentioned that at the tibiotarsal articulation is thrown oflf 

 a very fine cord, which is directed outwards, and forms the external dorsal collateral 

 of the first toe. Each of its tliree terminal branches courses along an intermetatarsal 

 space, and at the metatarso-phalangeal articulations separates into two filaments, 

 whence results the following distribution : the external branch forms the internal 

 dorsal collaterals of the first toe and external of the second ; the middle constitutes 

 the internal dorsal collaterals of the second toe and external of the third ; lastly, the 

 internal furnishes the internal dorsal collaterals of the third toe and external of the 

 fourth. The anterior tibial nerve accompanies the artery of that name, descends along 

 the external face of the tibia, and termiuiites in two branches at the tarsus. Of these, 

 one is distributed to the tarsal articulations and the pedal muscle ; the other, internal, 

 enters the intermetatarsal space, and at the corresponding metatarso-phalangeal joints 

 anastomoses with the internal branch of the musculo-cut;meous nerve, and is lost in tlie 

 same parts. The internal poplitetts forms the second terminal branch of the great sciatic 

 nerve, and in the Dog and Cat represents that portion of the latter which, in the Horse, 

 is situated behind the femoro-tibial articulation. It is continued by the posterior tibial 

 nerve, which terminates by the two plantar nerves. During its course, the external 

 popliteal furnishes articular and muscular filaments, as well as cutaneous twigs 

 subsequently; among the latter may be mentioned the external saphenous, which arises 

 by two branches, and is expended behind the malleolus, at the outer side of the tarsus. 

 The plantar nerves are external and internal ; the latter lies at the inner border of the 

 tendon of the superficial flexor muscles of the phalanges, and when it joins the middle 

 of the metatarsus, it detaches a fine filament that forms the internal plantar collateral 

 of the fourth toe ; it then passes obliquely towards the first toe, at the deep face of the 

 above-named tendon, and successively gives off three filaments — one for each inter- 

 metatarsal space. These filaments anastomose with the terminal branches of the 

 external plantar, at tlie metatarso-phalangeal articulations; the first two filaments 

 supply the large cushion of the paw. 



The external plantar nerve passes between the two flexor tendons of the toes, where 

 it gives a filament that constitutes the external plantar collateral of the first toe. It is 

 afterwards placed outside the deep flexor, then enters beiieath the short flexor and 

 divides into several branches, muscular and digital. Each of the latter, three in 

 number, passes into a corresponding interosseous space and bifurcates at the metatarso- 

 phalangeal articulations, receiving filaments from the internal plantar, and forming the 

 following plantar collaterals : the internal of the first toe, internal and external of the 

 second, internal and external of the third, and external of the fourth digit. 



COMPARISON OF THE LDMBO-SAORAL PLEXUS OF MAN W^TH THAT OF ANIMALS. 



It is usual, in human anatomy, to describe a lumbar and a sacral plexus. 



The lumbar phxus is constituted by the anastomoses of the anterior branches of the 

 five lumbar nerves ;' these are united bv fine filaments, which are not intricatelv 

 associated. The divisions of this plexus are distinguished as collateral and terminal 

 branches. The first, destined to the upper part of the limb and the skin covering the 



(' Wilson says the four upper lumbar nerves and the last dorsal ; Heath gives the 

 same constitution.) 



