568 



THE ARTERIES 



the sacrum, external to the sacral chain of the sympathetic, and internal to the 

 anterior sacral foramina, crossing in its course the slij^s of origin of the pyriformis 

 muscle and the first anterior sacral nerve. On reaching the coccyx it anastomoses 

 in front of that bone with the middle sacral arter}', and with the inferior lateral 

 sacral of the opposite side. In this course it gives off: — Posterior or spinal 

 branches, which enter the second, third, and fourth anterior sacral foramina, and, 

 after supplying the spinal memliranes and anastomosing with each other, leave the 

 spinal canal l:)y the corresponding posterior sacral foramina, and are distributed to 



Fig. 369. — The Gluteal Region, with the Glvteal, Sciatic, and Prmc Arteries. 



(From a dissection by W. J. Walsham in St. Bartholomew's Hospital ^Museum.) 



The inferior gluteal branch of the sciatic artery has been drawn inwards over the tuber ischii with the 

 reflected origin of the gluteus maximus muscle. 



Gluteus medius, turned up 

 INFERIOR GLUTEAL NERVE , Gluteus minimus 



Gluteus maximus, cut 

 Internal circurnjlex artery 

 Obturator externus 



Insertion of gluteus medius 

 External circurnjlex aiteii/ 



}Iiiscii!ar branches of sciatic artery 

 Deep branch of gluteal artery 



.SUPERIOR GLUTEAL NERVE 



Pyriformis perforated by peroneal 

 portion of sciatic nerve 



Cut edge of gluteus maximus 



Puilii nitpjyand nerve and nerve 

 to obturatoi internus 

 Sciatic artery 



Insertion of 



gluteus maximus 



First perforating arferi/ 



Quadratus femoris 



Branch of internal cirrumjleT artery 

 Obturator internus with 'the two gemelli 



I Semi-tendinosus 

 Semi-membranosus 



LESTER SCIATIC NERVE 

 Arteria nerri comes ischiatici 

 POPLITEAL PORTION OF GREA TSCIA TIC NER VE 

 I LONG PUDENDAL NERVE 

 PERONEAL PORTION OF GREAT SCIA TIC NERVE 



the muscles and skin over the back of the sacrum: anterior or rectal branches 

 which run forward to the rectum; external branches which are distri))uted to the 

 pyriformis, coccygeus, and the sacral nerves; and internal branches wliich pass 

 inwards across the sacrum to anastomose with l)ranches of the middle sacral artery. 

 At times the lateral sacral arteries are exceedingly small, the spinal branches 

 then coming chiefly from the middle sacral. The anastomosing branches between 

 the lateral sacral and middle sacral are usually regarded as sacral arteries dimin- 

 ished in size, and serially homologous with the lumbar and intercostal arteries. 



