496 



SHEEP HUSBANDRY IN THE SOUTH. 



left side of the latter. It communicates with the pharynx, which commu- 

 cates with the mouth. The food on being swallowed enters the pharynx 

 or food bag, which is directly above the larynx — so that the food traverses 

 the entrance to the latter. It is deterred from enteiing the windpipe by 

 the epiglottis, a triangular lid or valve which projects upward from the 

 floor of the passage, and which closes upon and covers the glottis, or en- 

 trance into the windpipe, when any substance more dense than air comes 

 in contact with it in its downward passage. 



The Thyroid and Parotid Glands. — The Thyroid glands are located 

 on each side of the trachea. The parotid glands are situated immediately 

 below the ear, behind the angle of the lower ja^v. There are certain 

 other glands situated beneath the lower jaw, not necessary here to be re- 

 ferred to. 



THE HEAD AND ITS CONTENTS. 



Fig. 49. 



BONES OF THE HEAD. 



1. The nasal bone. 



2. The upper jaw bone. 



3. The intermaxillary bone, which supports the 



pad which supplies the place of upper front 

 teeth. 

 4.4. The frontal pinus. 



5. Cavity or sinus of the horn, communicating 



with the frontal sinus. It is here shown by 

 the i-emoval of a section of the base of the 

 horn. 



6. The parietal bone. 



7. The frontal bone. 



8. Vertical section of the brain. 



9. Vertical section of the cerebellum. 



a. The cineritious portion of the brata. 



b. The medullary portion. 



10. The ethmoid bone. 



1 1. The cribriform or perforated plate of the ethmoid 



bone. " It separates the nasal cavity from the 

 brain ; it is thin almost as a wafer, and pierced 

 by numerous holes, through which the olfacto- 

 ry nerve penetrates, in order to spread itself 

 over the inner part of the nose." 



12. The lower cell of the ethmoid bone. 



13. The superior turbinated bone. 



14. The inferior turbinated bone. 



17. The sphenoid bone. 



The above cut, copied from Youatt, gives, with the subjoined explana- 

 tions, a sufficient description of most of the structures of the head. Some, 

 however, demand a little more particular description. 



The Brain. — The brain of the sheep is smaller in proportion than that 

 of Man, but is shaped so nearly like the latter, and so closely resembles 

 it in its general structure and conformation, that it furnishes the medical 

 student with a good substitute for the brain of the human subject ! The 

 brain is invested in a membrane called the j^ia mater. The cranium or 

 skull is lined by the dura mater, and between this and the former there is 

 a delicate membrane called the tunica arachnoidcs. 



The Nerves. — Ten pair of nerves arise from the brain, and thirty pair 

 from the spinal cord. These supply the sense of seeing, hearing, tasting, 

 smelling, feeling, &c. &c. ; and a portion of them, termed nerves of mo- 



(936) 



