DISSECTION OF THE HEAD AND NECK. 151 



ing the alveoli of numerous mucous glands, whose ducts penetrate the 

 mucous membrane. It forms a very loose bond of connection between 

 the muscular and mucous layers; and when the ojsophagus is cut 

 across, the mucous coat appears almost as if it lay independently 

 within the muscular layer. 



The Mwous Membrane has a thick stratified epithelium ; and, except 

 during the act of deglutition, its free surface is thrown into longitudina] 

 folds which meet with one another and obliterate the lumen of the tube. 

 In colour it is whitish, owing to its low vascularity and the thickness 

 of its epithelial covering. 



THE UPPER PART OF THE NECK. 



Position. — The animal should be suspended in imitation of the natural 

 standing posture, in the manner described at page 8, for the dissection 

 of the outer scapular region. 



Directions. — The whole of the neck behind the atlas should be 

 denuded of skin. The cutaneous nerves of the region should then be 

 noticed, and the spinal accessory nerve should be found crossing obliquely 

 backwards and upwards on the surface of the splenius muscle. 



Cutaneous Nerves. For the most part, the cutaneous nerves of this 

 region are derived from the stellate groups already seen perforating the 

 mastoido-humeralis. These are derived from the inferior primary 

 branches of the cervical spinal nerves from the 2nd to the 6th. Other 

 branches, which are derived from the superior primary branches of the 

 same nerves, emerge near the middle line of the neck above, and are 

 distributed to the integument beneath the mane. 



The Spinal Accessory (11th Cranial) Nerve (Plate 27). This 

 nerve derives its fibres from the medulla oblongata and the cervical 

 part of the spinal cord.' It leaves the cranium by the foramen lacerum 

 basis cranii, passes backwards on the guttural pouch, turns upwards 

 over the edge of the wing of the atlas, and passes obliquely backwards 

 and upwards beneath the mastoido-humeralis muscle. Appearing at 

 the upper edge of the last-named muscle, it is continued in the same 

 direction on the surface of the splenius, and disappears beneath the 

 cervical trapezius, in which and the dorsal trapezius it terminates. 

 While the neck is elevated, the trimk of the nerve is thrown into 

 numerous short sinuosities, apparently to obviate stretching of the 

 nerve when the neck is depressed. 



Directions. — The cervical portions of the trapezius and rhomboideus 

 muscles should now be examined in co-operation with the dissector of the 

 fore limb ; and, thereafter, the mastoido-humeralis is to be dissected. 



The Trapezius. See page 9. 



The Rhomboideus. See page 10. 



The Mastoido-Humeralis, or Levator Humeri (Plates 27 and 28). 



