Dissection of Sheep^s Head. 253 



Dissection of Mouth, Tongue, Palate, Posterior Nares, 

 Pharynx and Larynx. The Student should now take a saw, 

 without a back, and make an antero-posterior vertical section 

 of the Head ; carrying the incision right through the base of 

 the Skull down to the level of the posterior part of the Thy- 

 roid Cartilage and the dorsum of the Tongue. The two halves 

 may then be laid out on each side, like the leaves of a book, 

 leaving the Tongue in the middle line. 



The osseous frame-work, within which are contained the 

 several parts and organs next to be described, demands the 

 first attention. The upper part of the cranium, or brain- 

 case, was removed in an early stage of this dissection ; but 

 the longitudinal central axis, above which are the brain, nose 

 and face, and below which are the posterior nares and the 

 palate, still remains. Posteriorly, and forming the support 

 of the Medulla Oblongata, will be seen, in section, the anterior 

 boundary of the foramen magnum, formed by the Basi-occi- 

 pital factor of the occipital bone ; this is about an inch long : 

 then follows the 'body' of the sphenoid bone, or Basi-sphenoid, 

 limited anteriorly by a suture (in appearance a greyish line) , 

 and hollowed out superiorly to receive a pink oval body : the 

 hollow is known as the sella turcica : the pink oval gland 

 depending from the brain, just posterior to the Optic com- 

 missure, is the pituitary body. Next, anteriorly, is a rather 

 broader bone, notched superiorly by the groove in which is 

 lodged the optic commissure ; and terminated anteriorly 

 by the upright perforated bone through which the olfac- 

 tory nerve fibres penetrate ; this is the Pre-sphenoid. The 

 Basisphenoid and Presphenoid form in man two of the 

 factors of the ' Sphenoid bone.' The anterior boundary of 

 the cranial cavity is formed, as just said, by the perforated 

 Ethmoid bone, and next above that come the cells in the 

 Frontal bone. Thus the floor of the Cranial cavity is seen 

 to be made by the following bones, arranged serially, mz.. 



