DISSECTION OF THE ANTERIOR LIMB. 9 



posterior half of the shoulder. The skin, it will be observed, is thicker 

 than in the pectoral region, and it has the panniculus carnosus attached 

 to its inner surface. Care must be taken not to remove this panniculus 

 with the skin. 



The Panniculus Carnosus is the muscle which enables the horse to 

 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 scapulohumeral 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 

 muscles, distinguished as the cervical and the dorsal trapezius. 



The Cervical Trapezius (Plate 4) arises from the funicular portion 

 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 Trapezius (Plate 4) is continuous with the preceding 

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

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

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

 the rhomboideus. 



