426 



THE MUSCULATURE 



blend with the fundiform (suspensory) hgament and fascia of the penis and the dartos and sep- 

 tum of the scrotum. 



Muscle fasciae and sheaths. — The posterior serrate muscles (fig. 380) are enveloped by two 

 adherent layers of an aponeurotic sheet that extends as a single membrane between them and is 

 attached lateralward to the ribs and medialward to the spines of the thoracic vertebrae. The 

 membrane between the muscles may represent the rudiment of a primitive continuous muscle 

 such as is found in some lower vertebrates. This membrane may usually be easily separated 

 from the aponeurosis of the latissimus dorsi on its superficial surface and the lumbo-dorsal 

 fascia beneath. 



The intercostal muscles are covered by delicate, adherent membranes on each surface. 

 The external intercostal muscles are continued as aponeurotic bands between the^costal cartil- 

 ages. These serve here as fasciae for the internal intercostals. 



Fig. 385. — The Intercostal Muscles. 



The external oblique muscle is covered externally by a dense, adherent membrane and in- 

 ternally by a more delicate membrane except where the muscle is attached to the ribs or fused 

 with the external intercostal muscles. Ventrally and distally these membranes are fused be- 

 yond the fleshy portion of the muscle to the broad aponeurosis that serves to ensheath the rectus 

 muscle and cover the lower part of the abdominal wall (fig. 389). Dorsally the membranes 

 are in part attached to the ribs and in part are fused to form a membrane which becomes ad- 

 herent to the deep surface of tlie latissimus dorsi in the thoracic region and to the lumbo-dorsal 

 fascia in the liunbar region. 



The internal oblique muscle and the transversus abdominis have similar membranous 

 coverings which are fused to the aponeuroses of origin and insertion of these muscles. The 

 membranes on the mu.scles are, however, much more delicate than that of the external oblique. 

 More or less fusion between the two muscles with disappearance of the membranes covering 

 the opposing surfaces takes place, especially in the lower part of the abdominal wall. The super- 

 ficial muscle fasciie of the external oblique and the fascia) of the internal oblique are continued 

 into the thin cremasleric fascia which covers the cremasteric muscle, spermatic cord and testis. 



The diaphragm is covered on each surface by a more or less well-marked adherent membrane. 



The transversalis fascia is a thin membrane which lies external to the peritoneum of the ab- 

 dominal wall. It covens the peritoneal surface of the transversus muscle and its aponeurosis. 

 Ventrally it is continued across the median line internal to the rectus abdominis. In the lum- 

 bar region the fascia divides at the lateral margin of the quadratus lumborum (fig. 384), one 

 lamina of it passing dorsal to this muscle to be attached to the lumbo-dorsal fascia. The other 

 lamina extends over the ventral surface of the cjuadratus and becomes fused with the psoas 

 fascia. Proximally the transversalis fascia becomes fused with the fascial membrane adherent 



