The two rings do not correspond in direction, so that the length of the canal varies greatly when measured at different points. The inner angle of the internal ring lies almost immediately above that of the external ring, but the outer angle is situated five to six inches (ca. 12 to 15 cm.) from that of the external ring. The inner angles of the external rings are well defined and distinctly palpable in the living subject; they are about three to four inches (ca. 8 to 10 cm.) apart. =The Prepubic Tendon.=—The =prepubic tendon= is essentially the tendon of insertion of the two recti abdominis, but also furnishes attachment to the obliqui, the graciles, and the pectinei. It is attached to the anterior borders of the pubic bones, including the ilio-pectineal eminences. It has the form of a very strong thick band, with concave lateral borders which form the inner boundaries of the external inguinal rings. Its direction is oblique upward and backward.[54] Its structure is somewhat complex. Most of the fibers of the posterior part extend from one ilio-pectineal eminence to the other. The fibers which belong to the recti curve in to the median line. The aponeuroses of the internal oblique muscles are inserted into its abdominal surface, and the inguinal ligaments are attached to and continue across it in arciform fashion. The anterior part of the tendon of origin of the gracilis is fused with it ventrally, and many of the fibers of the pectineus arise from it. It gives off on either side a strong round band, the so-called =pubo-femoral= or =accessory ligament=, which is inserted into the fossa of the head of the femur with the round ligament (_vide_ hip joint). MUSCLES OF THE THORACIC LIMB I. THE MUSCLES OF THE SHOULDER GIRDLE (Figs. 177, 178, 179, 186) This group consists of those muscles which connect the thoracic limb with the head, neck, and trunk. The group naturally falls into two divisions—dorsal and ventral.[55] A. DORSAL DIVISION This division consists of two layers which overlie the proper muscles of the neck and back. FIRST LAYER 1. =Trapezius.=—This is a flat, triangular muscle, the base of the triangle corresponding with the spine. It is divided by an aponeurotic portion into two divisions: (=a=) =Trapezius cervicalis.=—_Origin._—The funicular portion of the ligamentum nuchæ, from the second cervical to the third thoracic vertebra. _Insertion._—The spine of the scapula and the fascia of the shoulder and arm. (=b=) =Trapezius thoracalis s. dorsalis.=—_Origin._—The supraspinous ligament, from the third to the tenth thoracic vertebra. _Insertion._—The tubercle of the spine of the scapula. _Action._—Acting as a whole, to elevate the shoulder; the cervical portion draws the scapula forward and upward and the thoracic portion draws it backward and upward.