OF THE ISCHIORECTAL REGION 455 



inch, its lower border being about a quarter of an inch from the external orifice. 

 It is paler in color and less coarse in texture than the External sphincter. 



Actions. Its action is entirely involuntary. It helps the External sphincter to occlude the 

 anal aperture. 



The Ischiorectal fossa (fossa ischiorectalis) (Figs. 334 and 344) is situated 

 between the end of the rectum and the ischial tuberosity. It is triangular in 

 shape; its base, directed to the surface of the body, is formed by the integument of 

 the ischiorectal region; its apex, directed upward, corresponds to the point of 

 division of the obturator fascia and the thin membrane given off from it, which 

 covers the outer surface of the Levator ani (ischiorectal or anal fascia). Its dimen- 

 sions are about an inch in breadth at the base and about two inches in depth, 

 being deeper behind than in front. It is bounded, internally, by the Sphincter 

 ani, Levator ani, and the Coccygeus muscles; externally, by the tuberosity of the 

 ischium and the obturator fascia, which covers the inner surface of the Obturator 

 internus muscle; in front, it is limited by the line of junction of the superficial 

 fascia with the base of the triangular ligament; and behind, by the margin of the 

 Gluteus maximus muscle and the great sacrosciatic ligament. This space is 

 filled with a large mass of adipose tissue, which explains the frequency with which 

 abscesses in the neighborhood of the rectum burrow to a considerable depth. 



The fascia covering the inferior surface of the pelvic diaphragm is known as 

 the anal fascia (fascia inferior diaphragmatis pelvis). It is attached above to the 

 obturator fascia along the line of origin of the Levator ani, while below it is contin- 

 uous with the deep layer of the triangular ligament and with the fascia on the Inter- 

 nal sphincter ani. The layer covering the upper surface of the pelvic diaphragm 

 (pars diaphragmatica fasciae pelvis) follows, above, the line of origin of the Levator 

 ani, and is therefore somewhat variable. In front it is attached to the back of 

 the symphysis pubis about three-quarters of an inch above its lower border. It 

 can then be traced outward across the back of the body of the pubis for a distance 

 of about half an inch, where it joins the obturator fascia. It is attached to this 

 fascia along a line which pursues a somewhat irregular course to the spine of the 

 ischium. The irregularity of this line is due to the fact that the origin of the Levator 

 ani, which in lower forms is from the pelvic brim, is in man lower down, on the 

 obturator fascia. Tendinous fibres of origin of the muscle are therefore often 

 found extending up toward, and in some cases reaching, the pelvic brim, and 

 on these the fascia is carried. 



MUSCLES AND FASCLffi OF THE UPPER EXTREMITY. 



The muscles of the upper extremity are divisible into groups, corresponding 

 with the different regions of the limb. 



1. OF THE THORACIC REGION. II. OF THE SHOULDER AND ARM. 

 1. Anterior Thoracic Region. 3 Acromial Region 



Pectoralis major. Pectoralis minor. ^ i, i 



Subclavius. 



2. Lateral Thoracic Region. 4 - Anterior Scapular Region. 



Serratus magnus. Subscapularis. 



