298 HUMAN EMBRYOLOGY AND MORPHOLOGY. 



2nd Lumbar. Psoas and iliacus, sartorius, pectineus, ad- 

 ductor brevis. 



3rd Lumbar. Adductors, quadriceps, obturator externus. 



4th Lumbar. Adductors, quadriceps, obturator externus, 

 also external rotators of hip, gluteus maximus, hamstrings. 



5th Lumbar. External rotators of hip, gluteus maximus, 

 gluteus medius and minimus. Muscles of leg and foot. 



1st Sacral. External rotators of hip, gluteus maximus, 

 gluteus medius and minimus. Muscles of leg and foot. 



2nd Sacral. External rotators of hip, gluteus medius and 

 minimus, flexor hallucis, extensors of foot and toes. 



3rd Sacral. Pyriformis, muscles of calf and sole. 



4th Sacral. Muscles of perineum. 



It will be remembered that the perineal region is developed 

 behind the limb buds of the lower extremities ; hence its nerve 

 supply from the most posterior nerve segments (3rd and 4th 

 sacral). 



Sherrington found that the posterior roots of the limb nerves 

 were distributed a regular and simple manner in apes. His 

 results are applied to the lower limb of a human foetus in 

 Fig. 240. The actual distribution in man, which has been 

 partially worked out by clinicians, varies considerably from what 

 might be expected from Sherrington's results (compare Figs. 

 240 and 241). 



In the human leg and foot there is a tendency for the nerve 

 fibres destined for the outer digits to proceed in the external 

 saphenous nerve instead of by the musculo-cutaneous. The 

 external saphenous nerve may supply the 4th and 5th digits, in 

 a manner similar to the ulnar nerve in the hand ; more fre- 

 quently it is confined to the outer side of the 5th digit. 



Pelvic and Shoulder Girdles. — In the basal part of each limb 

 bud a cartilaginous arch is developed. It consists of a dorsal 

 and ventral part, the joint cavity for the articulation of the limb 

 being situated at the junction of the two parts. Fishes retain 

 this simple primitive form of girdle. 



The Pelvic Girdle has undergone less modification from the 

 primitive type (Fig. 242) than the shoulder girdle. The primi- 



