CHAPTER IV. 



DISSECTION OF THE HEAD AND NECK. 



THE UNDER PART OF THE NECK. 



As the first stage in the examination of this region, the student should 

 dissect the structures placed below the cervical vertebrae — in other 

 words, the under part of the neck. 



Surface-marking. — A well-marked groove extends in the longitudinal 

 direction on the side of this region, beginning at the*upper part of the 

 neck, and terminating between the shoulder and the anterior part of the 

 pectoral region. It lodges the jugular vein, and is therefore termed the 

 jugular channel or furrow. In performing phlebotomy on this vein, 

 pressure is made on the furrow with the fingers, in order to arrest the 

 dowirward current of blood, and thus distend and make prominent the 

 vessel above the point of pressure. In the lower third of the furrow 

 the vein lies in company with the carotid artery, and it is in this situa- 

 tion that the latter vessel may be most conveniently exposed for ligature 

 or incision. The boundaries of the groove will be learnt after removal 

 of the skin. 



Position. — The dissection of this part of the neck should be completed 

 while the dissector of the fore limb is engaged with the pectoral region, 

 the animal being placed on the middle line of its back, and the head 

 being forcibly extended on the atlas in order to put on the stretch the 

 muscles and other structures to be dissected. 



Directions. — An incision through the skin should be carried along the 

 middle line, from the cariniform cartilage at the lower part of the neck 

 to the centre "of the intermaxillary space. From the latter point a 

 curved incision should be carried outwards a little behind the angle of 

 the jaw, as far as the wing of the atlas. These, in conjunction with the 

 incisions made by the dissector of the pectoral region, will permit the 

 skin to be reflected upwards as far as the middle of the side of the neck. 

 The cutaneous nerves and the cervical panniculus should then be 

 examined. 



Cutaneous Nerves of the neck. Five stellate groups of nerves will 

 be seen perforating the mastoido-humeralis muscle. These are derived 

 from the inferior primary branches of the cervical spinal nerves from the 

 2nd to the 6th The first of these appears behind the wing of the 

 atlas ; and, besides twigs to the upper part of the neck, it send^ into 



