130 



ANATOMY IN A NUTSHELL. 



The internal border is synoynmous with the outer boundary of the obtura- 

 tor foramen. 



The posterior border has the spine of the ischium a little below its middle. 

 This spine which extends backward and inward marks the lower limit of the 

 greal sciatic notch. It gives attachment to the Levator ani and (occygeus 

 muscles, externally to the Gemellus superior. Between this spine and the tuber- 

 osity is the lesser sciatic notch. The tuberosity has three surfaces — ex- 

 ternal, internal, and postero-inferior. 



The external SURFACE of the tuberosity is lost below in the ramus and 

 above with the groove for the tendons of the Obturator externus. It is limited 

 in front by posterior margin of the thyroid foramen, and externally by the pos- 



PLATE XLV. 



ARTICULAR 



PROCESS. 



SACRAL 

 FORAMEN 



ERECTOR 

 SPINA!. 



MULTIF1DUS 

 SPINA!. 



GLUTEU 



MAXI 



HIATUS 



SACRALIS, 



LEADING INTO 



SACRAL CANAL 



SACRAL CORNU 



GLUTEUS MAXIMUS 



SPHINCTER ANI 



COCCYX. 



Posterior View of Sacrum and Coccyx. 



tero-inferior surface. The muscks attached to this surface are the Quadratus 

 femoris on the posterior aspect, the Obturator externus on the antero-inferior 



aspect, and the Adductor magnUS below these two. 



The [NTERNAL SURFACE of the tuberosity extends to the thyroid foramen 

 in front. Behind and below it ends in a prolongation tor the attachment of 

 the greal sciatic ligament. 



The i'o-i bro-inferior surface of t he tuberosity has the Semimembranosus 

 attached to its upper and outer portion, while the Biceps and Semitendinosus 

 are attached to its lower and inner portion. 



The ramus of the ischium is not as long as the ramus of the OS pubis which 



