THE MUSCLES OF THE THORACIC LIMB 293 



ligament (vide hip joint). A band from the ventral surface extends backward and 

 blends with the tendon of origin of the gracilis on each side. 



The Muscles of the Thoracic Limb 



I. the muscles of the shoulder girdle (Figs. 266, 267, 268, 276) 

 This group (Mm. cinguli extremitatis thoracalis) consists of those muscles 

 wMch connect the thoracic limb with the head, neck, and trunk. It may be re- 

 garded as consisting of 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 which extends 

 along the supraspinous ligament. It is divided by an aponeurotic portion into two 

 parts : 



(a) Trapezius cervicalis. — Origin. — The funicular part of the ligamentum 

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



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 tuber spinee of the scapula. 



Action. — Acting as a whole, to elevate the shoulder; the cervical part draws 

 the scapula forward and upward and the thoracic part draws it backward and up- 

 ward. 



Structure. — The muscle arises by a narrow, thin aponeurosis, from which the 

 fibers of the flat fleshy part converge to the spine of the scapula and the aponeurosis 

 which separates the two portions. The cervical fascia joins the ventral edge of the 

 cervical portion to the brachiocephalicus, or the two muscles may unite or overlap 

 here. 



Relations. — Superficially, the skin and fascia; deeply, the rhomboideus, 

 latissimus dorsi, supraspinatus, infraspinatus, deltoid, splenius, serratus ventralis, 

 and anterior deep pectoral muscles, and the cartilage of the scapula. 



Blood-supply. — Deep cervical and intercostal arteries. 



Nerve-supply. — Spinal accessory nerve. 



Second Layer 

 This consists of three muscles — the rhomboideus, latissimus dorsi, and brachio- 

 cephalicus. 



2. Rhomboideus. — This consists of two parts: 



(a) Rhomboideus cervicalis. — Origin. — The funicular part of the ligamentum 

 nucha, from the second cervical to the second thoracic vertebra. 



Insertion. — The medial surface of the cartilage of the scapula. 



(b) Rhomboideus thoracalis (s. dorsalis). — Origin. — The spinous processes of 

 the second to the seventh thoracic vertebra by means of the dorso-scapular hga- 

 ment. 



Insertion. — The medial surface of the cartilage of the scapula. 



Action. — To draw the scapula upward and forward. When the limb is fixed 



the cervical part will elevate the neck. 



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

 logical sense; all the muscles of the group are ventral in the latter sense. 



