250 FASCIA AND MUSCLES OF THE HORSE 



surface of the ligament here by dehcate connective tissue, except where structures 

 intervene between the walls of the canal. Consequently the limits of the ring 

 are not very clearly defined. The external inguinal ring (Annulus inguinalis 

 subcutaneus) is a well defined slit in the aponeurosis of the external oblique 

 muscle, situated lateral to the prepubic tendon. Its long axis is directed from the 

 edge of the prepubic tendon outward and forward, and its average length is about 

 four inches (ca. 10 cm.). The canal contains in the male the spermatic cord, 

 the tunica vaginalis, the external cremaster muscle, the external pudic artery 

 and a small satellite vein, and the inguinal lymph-vessels and nerves. In the 

 female it contains the mammarj^ vessels and nerves; in the bitch it also lodges 

 the round ligament of the uterus, inclosed in a tubular process of peritoneum. 



The two rings do not correspond in direction, so tliat the length of the canal varies greatly 

 wlien measured at chfferent points. The inner angle of the internal ring lies almost immediately 

 above that of the external ring, Init the outer angle is situated five to six inches (ca. 12 to 1.5 cm.) 

 from that of the external ring. The inner angles of the external rings are well defined and dis- 

 tinctly 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 aLs(j furnishes attachment to the obliciui, 

 the gracilcs, and the ]7ectinei. It is attached to the anterior borders of the pul^ic 

 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.^ 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 

 femiu' with the rouml 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.^ 



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 funicidar portion of the ligamentum 

 nuchas, from the second cervical to the third thoracic vertebra. 



Insertion. — The spine of the scapula and the fascia of tlie shoulder and arm. 



' The obliquity of the tendon and the angle which it forms with the pelvic floor are of clinical 

 importance in regarfl to manipulation of the fretus in obstetrical cases. The slo])e varies in 

 different subjects. In some cases the tendon forms about a right angle with the pubic bones. 



^ The terms dorsal and ventral are here used in the topographic and not in the morpho- 

 logical sense. All the muscles of the group arc ventral in the latter sense. 



