148 THE ANATOMY OF THE HORSE. 



the intermaxillary space a branch which may be traced to near the 

 symphysis, and auricular branches which will subsequently be followed 

 to. the skin of the ear. Some branches from the lowest group turn down- 

 wards and backwards over the mastoido-humeralis in front of the 

 shoulder, and spread over the anterior part of the pectoral region 

 (Plate 1). The branches of the other- groups are disposed upwards, 

 downwards, and laterally, to supply the skin of the neck. 



Cervical Panniculus (Platysma my aides of man). This is the repre- 

 sentative in the neck of the muscle which is much more strongly 

 developed in connection with the skin over the trunk and shoulder. 

 It may be said to take origin at the lower part of the neck, where its 

 fibres are fixed to the cariniform cartilage (Plate 27). At this point it 

 is a band of considerable thickness ; but, as it passes up the neck, it 

 widens and becomes thinner. At the upper part of the neck its fibres 

 do not form a complete layer, but are scattered in an aponeurosis which 

 prolongs the muscle into the intermaxillary space and over the face. 

 Along the middle line it is joined by means of a. fibrous raphe to the 

 muscle of the opposite side. The outer edge of the muscle is continued 

 by an aponeurosis over the mastoido-humeralis, splenitis, and trapezius 

 muscles. In the lower half of the neck the muscle is intimately 

 adherent to the inferior edge of the mastoido-humeralis, and a careful 

 dissection is necessary to separate them. It covers the jugular furrow 

 and the sterno-maxillaris, sterno-thyro-hyoideus, and subscapulo-hyoi- 

 deus muscles. It is supplied by the cervical branch of the 7th cranial 

 nerve, which should be found entering it at the upper part of the 

 jugular furrow, and running on the deep face of the muscle or in its 

 substance where it covers the furrow. 



Action. — The cervical panniculus, unlike the panniculus of the trunk, 

 is but slightly adherent to the skin, w T hich, therefore, it can twitch only 

 slightly. Its principal action seems to be to brace the muscles over 

 which it is spread, and by its adhesion to the mastoido-humeralis it 

 may aid in depressing the neck. 



Directions. — Beginning at the middle line of the neck, the dissector 

 should carefully remove the foregoing muscle. This will'expose the 

 jugular furrow lodging the jugular vein. After that vessel has been 

 examined, a little dissection will serve to separate the muscles in rela- 

 tion to the trachea. 



The Jugular Vein (Plate 27) is the large vessel which drains away 

 the blood from the head and the upper part of the neck. It is formed 

 by the junction of the superficial temporal and internal maxillary veins, 

 which unite at the deep face of the parotid gland, below and behind the 

 temporo-maxillary articulation. It passes outwards through the parotid, 

 and then lies in a groove on the surface of the gland ; but this part of 

 its cojurse is not to be examined at present. At the lower extremity of 



