SERRATUS POSTICUS SUPERIOR 411 



the middle layer of the lumljar fascia separates it from the erector spinse, and along 

 its inner border are placed the intertransversales. 



The transversalis fascia, -which lines the interior of the muscular portion of the 

 abdominal parietes, is a thin layer of connective tissue. It is best marked in the 

 lower jDart of the front of the aV^domen, where some of the muscular and aponeurotic 

 layers are deficient. Below, it is attached to the inner border of the whole length 

 of the crest of the ilium, and to the outer half of Poupart's ligament, where it 

 blends with the iliac fascia covering the iliacus muscle. Beneath the inner half of 

 Poupart's ligament it is somewhat thickened, and called the deep crural arch. 

 This is but loosely attached to Poupart's ligament, and the fascia is continued into 

 the thigh, where it forms the front of the sheath of the femoral vessels. Internally 

 to this, it is attached to the free margin of Gimbernat's ligament, and the inner end of 

 the ilio-pectineal line. Further inwards it is inserted along the ])osterior border of the 

 crest of the pubes. At the back of the linea alba it is continuous with the fascia 

 of the opposite side. Behind the lower part of the rectus muscle it is thickened, 

 and takes the place of the posterior portion of the sheath from the pubes to the 

 fold of Douglas. Above, it becomes thin and blends with the fascia covering the 

 under surface of the diaphragm; and behind, it is lost in the loose fat which covers 

 the posterior surface of the kidneys, together with the back of the ascending and 

 descending colon. 



About half an inch (1"2 cm.) above Poupart's ligament, half way between the 

 anterior superior spine and the symphysis pubis, it is perforated by the spermatic 

 cord in the male, and the round ligament in the female. To the margins of the 

 opening, which is called the internal abdominal ring, is attached a tubular pro- 

 longation, the infundibuliform fascia, which invests the cord or round ligament. 

 The connection of this tube to the rest of the fascia may be compared to the attach- 

 ment of the sleeve to a coat. No opening is therefore visible from the exterior 

 until the sleeve-like tube has been divided. 



MUSCLES OF THE BACK 



The first and second layers have already been described, as they belong to the 

 groups of muscles which pass from the thorax to the bones of the upper extremity. 

 The third layer consists of muscles which stretch in a nearly transverse direction 

 from the spinous processes of the vertebrae to the back of the ribs, viz. the serratus 

 posticus superior and the serratus posticus inferior. 



Third Layer 



1. SEPvRATUS POSTICUS SUPEPvIOR 



The serratus posticus superior — named from its saw-like edge and its relation 

 to the other serrati — is a cpiadrilateral sheet with a toothed outer margin. 



Origin. — (1) The outer surface of the lower part of the ligamentum nuchfe 

 near its posterior edge; (2) the spines of the last cervical and first two thoracic 

 vertebne. and the supraspinous ligament connecting them. 



Insertion. — The upper borders and outer surfaces of the second to the fifth ribs, 

 external to their angles. 



Structure. — The inner half is a tendinous sheet, the fibres of which run down- 

 wards and outwards, and when they have passed beyond the line of the transverse 

 processes they become fleshy and are inserted into the ribs by the lower borders of 

 the four teeth into which the muscle divides. 



