THE VENTRAL MUSCLES. 515 



The Sacro-Coccygeus Posterior. — The reduction of the caudal vertebrae in man, indicated 

 by the condition of the coccygeal vertebrae, has brought about a reduction of the terminal 

 portion of the dorsal axial musculature, it being, as a rule, represented only by the ligaments 

 upon the dorsal surface of the coccyx. Quite frequently, however, muscular fibres occur inter- 

 mingled with the connective tissue, and occasionally a distinct muscle, the sacro-coccygeus 

 posterior, may be found, extending from the last sacral vertebra or even from the greater sacro- 

 sciatic ligament to the coccyx. 



THE VENTRAL MUSCLES. 



The ventral trunk musculature includes all those axial muscles which are supplied 

 from the anterior divisions (ventral rami) of the spinal nerves. As already indicated 

 (page 473), it is divisible into three subgroups : a group of more median muscles, char- 

 acterized by their fibres retaining more or less perfectly a longitudinal direction and 

 constituting the rectus group ; a more lateral group, in which the fibres possess a 

 distinctly oblique or transverse direction, and may consequently be termed the 

 obliquics group ; and, finally, a hyposkelctal group, whose fibres have a longitudinal 

 direction, and which is situated anterior or ventral to the spinal column. 



Instead of considering the various muscles belonging to each of these groups in 

 succession, it seems more convenient to combine a topographic classification with 

 the morphological one, and to describe the various groups as they occur in the neck, 

 thoracic, abdominal, and perineal regions. It must be understood, however, that 

 the delimitations of these regions are somewhat arbitrarily chosen, and that there is, 

 so far as the muscles are concerned, a considerable amount of overlapping of certain 

 regions, portions of myotomes which strictly belong to the thoracic region, for 

 instance, being found within the limits of what is recognized as the abdominal region. 

 In many cases these overlapping myotomes have united with myotomes of the lower 

 region to form a continuous muscle, and it is consequently impossible to refer them to 

 their proper topographic position without doing violence to the individuality of the 

 muscles which they help to form ; but when they remain practically distinct from the 

 muscles of their adopted region, they will be referred to the region from which they 

 have come. 



It will be convenient to consider first the muscles of the abdominal region, there- 

 after taking up in succession those of the thoracic and cervical regions, those of the 

 perineal region being left until the last. 



THE ABDOMINAL MUSCLES. 



The Superficial Fascia of the Abdomen. — The superficial fascia of the 

 abdomen is usually described as consisting of two layers. These, however, are well 

 marked only over the anterior and especially the lower part of the abdominal wall, 

 losing their distinctness laterally and above, where they pass over into the superficial 

 fasciae of the back and thorax. The superficial layer {Camper s fascia) usually con- 

 tains a considerable amount of fat, except at the umbilicus, and may occasionally 

 reach a great thickness owing to the development of that tissue. The deeper layer 

 immediately underlies the fatty layer, and is a connective-tissue membrane of vary- 

 ing density, containing a considerable amount of yellow elastic tissue. It is con- 

 nected to the deep abdominal fascia which covers the muscles of the abdominal wall 

 by loose areolar tissue, except along the median line, where it is firmly adherent 

 along the linea alba and around the umbilicus. A short distance above the sym- 

 physis pubis it gives off a band which is largely composed of elastic tissue and is 

 inserted below into the fascia of the penis, forming the suspensory ligament of that 

 organ (Fig. 528). 



In the inguinal region the deep layer of the superficial fascia is especially well 

 defined, forming what has been termed the fascia of Scarpa. Laterally it passes 

 down over Poupart's ligament to unite with the fascia lata of the thigh, the super- 

 ficial vessels and lymph-nodes of this region lying between it and the superficial 

 layer. More medially it is continued down over the spermatic cord, becoming con- 

 tinuous below partly with the deep layer of the superficial fascia of the perineum 

 {fascia of Colles) and partly, after fusing with the superficial layer, which loses its 

 fat, with the dartos of the scrotum. 



