DISSECTION OF THE ANTERIOR LIMB. 9 



twitch its skin, and thus remove offending insects. It is most extensive 

 over, the thorax and abdomen, but it is here carried over the muscles 

 covering the scapula and humerus. Before the muscle passes on to 

 the limb, it sends an aponeurotic layer inwards between the limb and 

 the chest-wall. At its upper border this layer is provided with a small 

 tendon, which becomes inserted into the inner tuberosity of the humerus, 

 and which will be seen when the limb is dissected from the trunk. A 

 nerve will be seen ramifying in the scapulo-humeral part of the panni- 

 culus. This turns round the posterior border of the limb ; and, as 

 already seen, it is formed by the union of the subcutaneous thoracic 

 with some perforating intercostal nerves. 



Directions. — The panniculus is now to be dissected away from the 

 limb; and in doing this in front, care is to be taken of the thin 

 cervical trapezius muscle, which might be mistaken for a portion of the 

 panniculus. 



The Trapezius in the horse has its muscular substance interrupted 

 by a tendinous portion, and is therefore sometimes described as twO 

 separate miiscles, distinguished as the cervical and the dorsal trapezius. 



The Cervical Trapezius (Plate 4) arises from the funicular por- 

 tion of the ligamentum nuchse ; and it is inserted into the tubercle on 

 the spine of the scapula, while its most anterior fibres are continuous 

 with an aponeurosis covering the scapular muscles. Both the deep and 

 the superficial face of the muscle have a thin, adherent, fibrous covering, 

 the direction of whose fibres is at right angles to that of the muscular fibres. 



Action. — It draws the scapula forwards and upwards. 



The Dorsal Teapezius (Plate 4) is continuous with the preced- 

 ing by the aponeurotic centre already mentioned. It arises from the 

 summits of a few of the anterior dorsal spines, and is inserted into the 

 tubercle on the scapular spine. 



Action. — It pulls the scapula backwards and upwards. 



Directions. — Both divisions of the trapezius are now to be severed 

 close to their origin, and reflected downwards ; and while this is being 

 done, search is to be made for the branches of the 11th, or spinal 

 accessory, nerve, which enter their deep face. The muscles which were 

 covered, whoUy or in part, by the trapezius, will now be exposed. 

 These are : the splenius, the levator anguli scapulee, the supraspinatus, 

 the infraspinatus, the anterior deep pectoral, the latissimus dorsi, and 

 the rhomboideus. 



It will be remembered that in the dissection of the pectoral region 

 the anterior deep pectoral could not be followed to its termination. 

 The reflected portion of the muscle is here seen (Plate 4), but is partly 

 covered by the insertion of the mastoido-humeralis. 



The Latissimus Dorsi (Plate 4). Though neither the origin nor 

 the insertion of the muscle is found here, attention should be given to 



